Chapter 1: Test Chamber 00

After you fall through the glass, you appear in the room where you started Portal 1. The voice will talk for a while, during which time you can put the clipboard in the toilet or whatever. After a while, a portal will open in the room, so go out.

Go around the corner and go through the door. Pick up the cube and put it on the red button. Then go through the slightly broken door and continue on to reach the elevator. Go in.