In this next chamber, GlaDOS introduces you to Discouragement Redirection Cubes.
Discouragement Redirection Cube
Up ahead, you can follow the on-screen instructions to jump over the deadly laser, or you can just use the portal gun to get past it. Then go to the left and look into the walled-off area.
There is a Discouragement Redirection Cube in the corner, just as GlaDOS said. However, it's behind some pieces of metal. Just use portals to get the cube into the main area. You can press the button in the cube's original area if you want to destroy the current cube and make a new one drop from the ceiling.
When you hold the cube, if you put the cube into the path of a laser, the cube will redirect the laser (i.e. the "discouragement") away from you. The cube always rotates automatically whenever you pick it up such that it always redirects the laser away from you. If you drop the cube while it's still in a laser's path, it will keep redirecting the laser whichever way it was when you dropped it.
To open the path to the exit, simply use the laser redirection cube to make the laser point into the laser receiver on the wall. This will make some stairs rise up that lead to the exit. You can use portals to reach the stairs, or just jump over the laser.
Once you are up there, you have to press the red button to make the exit door open. However, the door will close if you don't keep stepping on it, so you have to put something there. Just create a portal on the floor nearby and a portal of the other color under the laser redirection cube to bring it to this area and put it on the button. Go through the exit and down into the elevator.