Test Chamber 03

After you receive the Portal Gun, you reach Test Chamber 03.

You reach Test Chamber 03 after you receive the Portal Gun.

Mind the Gap

Make your way through the room and you will find a gap. Place a blue portal somewhere and go through it to emerge beyond the gap.

There is another gap between you and the elevator. Create a blue portal near that elevator, then walk through the orange portal to reach the elevator. It will take you to Test Chamber 04.