Complete the chamber up to the point where the Chamberlock door opens.
Fire a portal through the door at the wall or floor in the secondary room.
Next throw a cube through the orange portal.
If you are unable to get the perfect momentum and angle to throw a cube through the portal use this method:
Grab a cube and jump up at the platform with the orange portal and without letting the cube go get it on the platform.
Attempt to move the cube through the orange portal.
If done correctly GLaDOS will say "You’re not a good person. You know that, right?", the Chamberlock will be opened and both buttons will freeze, making them unpressable.
Once entering the Chamberlock the game will resume.