The simplest way is:
ppython main.py
If you want to play a specific level : just pass its name as the first argument to main.py (without the .lvl extension). For example:
ppython main.py level3
Your goal is to reach the exit in each level. The exit is a big white sphere. You can use “portals” to go from one point of the level to another unreachable point. Just create a portal where you want to go, create a portal near you, go into the portal and “tadam” you’re on the other side.
Here are the available keys (AZERTY keyboard by default, change this in Gate/constants.py if needed):