Hi, I know this is a bit too basic, but I’ve never done compositing in my life and I was wondering what it is used for; thanks in advance 
It can be used for alot of things.
I use it for:
Compositing CG on Live-action
Lightsabers
Compositing is mainly used for CG/Live Action integration. And lightsabers. .
It can also be used for straight video editing. For example, doing a chromakey (green screen) shot. I’ve also used it for special effects where I isolate one object in a video clip with Claxa and use the resulting mask to recombine the isolated object with the background. One example would be to let the isolated object retain its original color but turn the rest of the clip to balck and white.
I see… This opens a whole new window of possibilities; I’ll start learning how to do it right now!!!