This is a fairly straightforward chapter, requiring no real "puzzle"; accommodate yoursef in the Portal environment. Follow the simple instructions and go through the portal when it opens. Note how the portal works; it is specifically placed so you can see yourself going in while on your way out. Go through the door and wait for the cube to drop from the dispenser. Press E to pick it up and place it squarely on the button. You will be introduced to the particle grid that prevents you from carrying things from level to level. Enter the lift and wait for the first real Testchamber to load.

Portal Walkthrough