Test chamber 1
Player 1: Place a portal at the end of the light bridge, then anywhere on the wall to your left. This will create a bridge over the dangerous water that you can both cross. Jump down to the platform below and then place an exit portal on the wall panel in the left corner near the water directly in front of you.
Player 2: Follow Player 1 and, as soon as you step onto the second light bridge, find two wall panels in the far right corner. Place a portal on each of them so that the bridge extends above your heads, crossing the water to your left. Jump off the light bridge and head to the second part of the test.
Part 2
Player 1: As soon as you enter the room, turn right and activate your first portal on the light bridge in the upper left corner of the room. Now have Player 2 hit the Arial Faith Plate in the center of the room, and once they touch the roof, shoot a portal at the wall in front of you to create a bridge for Player 2 to land on.
Player 2: Turn around to face the exit and create your first portal where the light bridge meets the wall, then turn around and place a portal directly under the light bridge in the upper left corner of the room. Go through both portals and hit the switch hidden in the corner (it's in an alcove to your right).
Player 1: A round, weighted ball will fall from the flask, so grab it and then orient yourself before standing next to the Arial Faith Plate.
Player 2: Fire a portal at the very top of the room (so it covers the blue force field), otherwise you will vaporize the ball needed to exit the level. Once Player 1 stands on the Faith Plate and headbutts the Light Bridge, a portal will immediately appear underneath them for them to land on.
Player 1: Turn around, walk towards the exit, throw the ball into the receiver in the corner of the room and walk through the now open exit with Player 2.
Test chamber 2
Player 1: Place your first portal on the wall panel directly ahead of you at the start of the test chamber, and place your second portal on the wall to the left of it. This will create a light bridge across the water, allowing Player 2 to complete their next objective.
Player 2: Run to the end of the light bridge and turn left. Launch your first portal on the wall directly ahead, then return and stand on the permanent light bridge and replace Player 1's portal with your second.
Player 1: Follow Player 2's new path and, at the end of the light bridge, find a panel on the wall ahead and to your right. Place a portal here and return to the start of the permanent light bridge. Place a second portal on top of Player 2's portal, creating a new path.
Player 2: The final part is pretty simple: place a portal at the end of the new light bridge, look to the right, and create an exit portal here. Go through it and follow Player 1 to the exit.
Test Chamber 3
Player 1: Place a portal on any of the side walls, then fire the portal at the wall next to the red piston next to the permanent light bridge. Ask Player 2 to join you on the light bridge and prepare for the next part.
Player 1: Turn right and make sure you've opened a portal at the end of the light bridge where the wall is, then open a second portal on the two-part wall panel opposite the funnel where the weighted ball is falling.
Player 2: Once the light bridge is positioned directly under the vortex, stand under the vortex and, as soon as Player 1 hits the red piston, catch the ball as it falls. Now join Player 1 and return to the permanent light bridge.
Player 1: Remove the portal from under the vortex and position it so it returns you to the entrance of the test chamber.
Player 2: Pass the weighted ball to Player 1, then place a portal on the wall in front of you, then place a second portal on the overhanging wall panels closer to the ceiling. This will create a light bridge that will lead you directly across the water to the exit.
Player 1: Carry the cargo across the light bridge, drop down to the round cargo rest area and lower it to reveal the panels in the second part of this chamber.
Part 2
Player 1: Upon entering the second part of the test chamber, look up and to the left. You'll see a light bridge cutting into the wall. Raise your first portal here, then place your second portal on the wall panel on the left side of the room (facing the exit). Try to make the light bridge form a small "step" toward the exit.
Player 2: Fire your first portal at the right wall where the light bridge approaches the exit area, then place your second portal on the far right side of the ceiling. This will create a vertical light bridge barrier that will descend into the water.
Player 1: Stand on the Arial Faith Plate, and the vertical barrier should prevent you from landing on the other side of the room. Simply jump to the exit. But if you find your bridge is too low, you can adjust its height slightly to boost yourself. Now you just need to make sure Player 2 follows you to the exit.
Test Chamber 4
Player 1: Ignore the Arial Faith Plate on the ground for now, and instead place a portal on the wall where the permanent light bridge is. Now have Player 2 stand on the Faith Plate, and while they're flying up, fire a second portal at the bottom of the wall below Player 2. This will create a platform they can use to run up to the permanent wall portion of the light bridge.
Player 2: Replace Player 1's portal with your own at the top, and then have Player 1 stand on the Faith Plate. Just like you did, you need to fire an exit portal at the bottom of the wall so the light bridge passes underneath them. Once Player 1 joins you at the top, look back at the slanted panel on the wall in the distance and fire a portal at the top. Now place a second portal at the end of the light bridge you're both on, and this will create a passage.
Player 1: Follow Player 2 through the portals, and you'll run up a slanted path onto a platform that leads to the second half of this test chamber.
Part 2
Player 1: This is similar to the first half of the test chamber, except instead of going up, you need to go down. So, place a portal on the panel at the end of the light bridge, then below you on the panels going straight down, and activate the second portal here. Player 2: Stay put while Player 1 does the next steps.
Player 1: Go through the portal you created to the chasm at the far end. If you turn 90 degrees to the left and look down, you should notice a series of panels on the wall you can shoot. Drop down here, and a new light bridge should appear directly below you (preventing you from falling into the deep, dark chasm below). While Player 2 stays put, walk up to the wall, then turn 90 degrees to the right, you should see three panels lined up under a white exit sign. Place a portal on the middle panel and follow it until you notice the metal floor panels beneath you flip over.
Player 1: Look to the far right and there's a working panel behind the slanted panel directly behind the camera. Bring out your light bridge and it will reach where you are now.
Player 2: You need to shoot a portal on the slanted wall next to Player 1 (it's to the right and above where the light bridge will be), and a second portal below you on the single panel.
Player 1: Run along the light bridge until you're directly above the portal below you. Once you're sure you're ready, turn around and face Player 2 and shoot a portal in the wall above and to your right. This will cause you to fall through the portal and climb out through the second slanted portal directly to the exit!
Player 1: Once here, replace the light bridge on the same wall it was on just before and have Player 2 stand directly above the portal you just fell into. When they're ready, shoot the portal on the wall next to or below you and watch as Player 2 flies through the air straight toward you and the exit.
Test Chamber 5
Player 1: There's an Arial Faith Plate on the floor to your right at the start of this test chamber, so place your portal on the ceiling above it, then on the far left or right side of the floor opposite (there's a permanent light bridge in the center). Jump off the Faith Plate and head to the light bridge. Launch the portal into the wall next to the light bridge, and remember which color portal you used!
Player 2: Once Player 1 reaches the light bridge, place your portal on the raised square panel in the top left corner of the floor, and the next portal above the faith plate.
Player 1: Stand on the Faith Plate and, as you ascend/descend, shoot through the portal on the vertical wall in the distance to create a bridge directly below you. Approach the wall and wait for Player 2 to appear.
Player 2: Place one portal above the Faith Plate and place the second one either to the left or right of the floor opposite the Faith Plate. Now activate the plate, landing at the light bridge and joining Player 1 through the portal.
Player 1: Have Player 2 jump from the light bridge onto the ledge to your right. Turn right, facing the wall, and place another portal on the light wall. Now place the light bridge on the lower section so you fall onto it. Have Player 2 follow you to the end, where you can both jump into the alcove leading to the second part of the test chamber.
Part 2
Player 1: Your first portal should instinctively be placed on the wall where the light bridge is stopped, now place another portal on the panel below and to the left (this one will be much closer to the water).
Player 2: While Player 1 is preparing the light bridges for you, you need to place a portal on the slanted panel to your left, and then directly above the springboard. Activate the Faith Plate and you will land in the square area directly above Player 1. Launch a portal in the slanted wall here, and then jump down onto the platform with the light bridge that Player 1 created for you earlier. Now place the entrance portal back above the Faith Plate before stepping on it. This will send you flying across the water to the upper ledge in the far right corner of the room. Once you land, you need to place a portal here on the slanted panel.
Player 1: Look up to where Player 2 is now, and on the right wall (to the left of the light bridge) there is a panel you can shoot. Launch a portal there so that your light bridge appears near the upper ledge.
Player 2: Descend the light bridge, but stop when you reach the permanent version. Have Player 1 place the portal back on the lower panel (near the water) and use it to return to the start. For the final time, place the entrance portal directly above the Arial Faith Plate.
Both players: Step onto the ramp and you'll both fly toward the exit and into the next test chamber!
Test Chamber 6
Player 1: The main goal here is to prevent the turrets from hitting you along the narrow corridor. So, first, you need to create a portal on the wall with the light bridge on it, and then on the wall to the right of the stairs (it's right in front of you). This will block the turrets from the right.
Player 2: You need to launch your portal immediately to the left of the stairs, and then on the wall to your left.
Player 1: Repeat the same step as in the first part (place the bridge light barrier on the wall next to the stairs). This applies to the right set of turrets.
Player 2: Place your portal on the wall where Player 1's barrier ends, then place a second exit portal on the other wall next to the stairs, creating a barrier that now covers both sides! Climb the stairs with Player 1 and reach the second section!
Part 2
Player 1: Drop down onto the bridge below you and place your first portal on the wall to your left, then turn 180 degrees and look at the platform directly above you. Have Player 2 follow you here, where you both need to stand in the alcove to avoid the turrets.
Player 2: Look for the second light bridge near the ceiling in the center of the room. Place a portal where it meets the wall, then activate the portal directly behind you. This will create a vertical barrier protecting you from gunfire.
Player 1: Replace your bridge below you with the one in front of you, placing a portal on the panel behind you. This will create a bridge directly to the other side, while Player 2's vertical bridge will still provide much-needed cover from those pesky turrets. Run across the bridge (with Player 2 in tow) and have them run to the other side and wait for you. Stand in front of the vertical beam (facing the red piston) and have Player 2 remove the vertical shield in front of you. Without hesitation, run forward, press the button, and then reverse so you're directly under the funnel (allowing you to catch the ball as it falls).
Player 2: Once Player 1 has moved far enough away, immediately replace the vertical light bridge in front of him to prevent the turrets from tearing him apart!
Player 1: Now it's just a matter of carrying the ball over the water, dropping it at the designated spot, and leaving with Player 2 through the now-familiar exit!
Test Chamber 7
Player 1: Stay behind the glass panel on the right (to avoid being seen by the turret), find a portal in the wall near the light bridge below, and then fire a shot at the bottom of the wall in front of you. This will create a protective barrier for Player 2.
Player 2: Now you have a chance to place a portal on the wall ahead, then into the alcove directly above and to your left.
Player 1: As soon as you notice Player 2 passing through the portal, raise the height of your defensive barrier to prevent the turret from killing your partner.
Player 2: Create a portal on the ceiling directly above the Faith Plate, and then another one on the inclined panel to the right of the turret. Step on the ramp and watch as you knock the turret over!
Player 1: Follow in Player 2's footsteps and reach the area with the Faith Plate. Step on it, and you too will be transported across the chasm to the second part of this room.
Part 2
Player 1: Upon entering the second section of the test chamber, you'll notice several turrets guarding the area to your right. Your first task is to get a portal on the left column with a turret on it, and then a second portal about two-thirds of the way down the vertical concrete column directly in front of you. This will create a barrier high enough to protect both of you.
Player 2: Wait for Player 1 to stand on the large red button on the ground, and when they do, look up toward the middle of the ceiling where a concrete panel will drop. Shoot it, and then shoot the panel behind you. This will cause you to fall into the middle of the room, directly behind the first two turrets. Now you need to shoot the portal on the panel above and to your left (actually, just above the left turret). Make sure Player 1 is ready, then turn around and press the red button.
Player 1: Back away as soon as Player 2 presses the button, as you need to catch the companion cube before it bounces off the wall and falls into the nearby toxic water. Once you have a firm grip on it, place the cube on the button and wait for Player 2 to shoot a portal on your side and on the panel above it (or you can even do this yourself if you prefer), then walk through it to join your friend on the other side.
Player 2: Once your colleague has joined you, you need to place a portal back on the left hanging panel (above the turret), and another one on the irregular column to the left (directly opposite the turrets). Now, either you or Player 1 needs to press the button to release balls and cubes, knocking down both sets of turrets!
Both players: Now it's just a matter of heading to the exit and the last test chamber on this course!
Test chamber 8
Player 1: As soon as you cross the metal walkway in the building ahead, enter the force field to your left and immediately face the pipe on the left. Now grab the ball and face the wall behind you.
Player 2: Upon entering the building, place your first portal on the wall directly next to the "overriding" beam, then shoot it through the metal grate at the top of the wall (where Player 1 is currently located). Go through the portal, grab the ball from Player 1, and place it in the slot to open the path to Part 2.
Part 2
Player 1: Run along the road, turn left towards the blue force field and run along it. Find the slanted panel on the right (it has a yellow border) and place your first portal. Now look above you and you should notice a second panel you can shoot (again, with a yellow border). Place your second portal on it.
Player 2: Your job is to stay away from the force field and instead focus on the horizontal light bridge located on the left. You will need a portal on the wall it hits and a second portal on the vent directly above your head (still behind the force field). This will create a barrier that will catch the ball as it flies into it and throw the ball into the portal created by Player 1 a few seconds ago.
Player 2: Once the ball hits the vertical barrier of the light bridge, you must quickly open a portal on the slanted panel in the lower right corner (near where Player 1 passed through). This will create a tilted light bridge that will catch the ball and control it as it rolls to a permanent light bridge nearby.
Both players: Either one of you must pick up the ball and follow each other down the road, up the stairs to your left, where you must throw the ball into the slot, into the hole, and open the third - and final - part of this course.
Part 3
Player 2: When you enter the final testing area, turn left and look for the wall marked "Bridge." Place a portal here, then place portal number two on the large square panel with a yellow border at the top and to the right. This will create a light bridge that spans most of the testing area. Ask Player 1 to join you as you go through the portal.
Player 1: Walk along the light bridge until you're directly above the square section of floor with the number "1" painted on it. Activate the portal on this section of floor to be directly above it. Now look for the slanted panel located above and slightly to the right, this is the exit, so place the second portal here.
Player 2: You need to wait for Player 1 to signal that they're ready, as there's an important task ahead. Position yourself so that you're directly above the panel with the number "2," now look for the slanted panel at the top and to the left. The next sequence of events requires you to act quickly, so make sure you aim quickly! Launch a portal onto the inclined panel, and you'll both begin falling to the ground. As you fall, you'll quickly create an entrance portal directly below you. If you're fast enough, you'll both collide in mid-air and land on the platform below.
Both players: Immediately after you finish the hugging scenario, go inside, find the disk on the top left table and insert it into the machine to complete Course 3!
Portal 2: Co-op Walkthrough:
Course 3: Solid Light Bridges
Source: gamerguides.com