I will be using Chamber 16 as an example.

Start by positioning yourself as close to the wall with the glass as possible. Look straight up, and shoot a primary portal as close to the wall aswell.

This part may be a bit tricky at first!
In the small space between the primary portal and the wall, shoot your secondary portal until the primary portal opens up. The orange portal should be on the other side of the wall.

You've done it, congratulations!
Move your primary portal onto a surface you can easy access, such as the floor. You can then skip the entirety of chamber 16, place a turret on the button, and complete the test.

If this was useful at all, any awards would be super appreciated. I am trying to level up! :)