\-WARNING- SPOILERS DETECTED/ READ AT OWN RISK-/
In the game you go through a series of tests that Aperature left out from the testing tracks. Your device is the "Paint Gun", a handheld device that shoots the two gels such as Repulsion Gel and Propulsion Gel. With these two you can send yourself flying through tests, there are some challenges with the device. If you over jump, "you're a dead test subject".
If you were to play this game, you will find out the opposite testing tracks that were never really included in the classic portal games. With the Paintgun in hand, you zoom and bounce through chambers with jumps and gaps that are not the safest things on this planet.
Be cautious about the replacement power core test, you literally have to break the speed limit. By doing so, you escape into a peaceful area that might seem real. But it isn't, when you reach the end of the area you are greeted with a door painted to look like part of the outside. If you never escape the replacement protocol, "you're a dead test subject".
I made this by listening to the Aperature Tag soundtrack by Harry101uk over and over again. I hope you enjoyed reading this extremely short preview on the portal 2 mod.