Issues with the freeware game Nexuiz, and just pc games in general?

I’ve never been into playing PC games, and I just downloarded Nexuiz off of apple’s website, (and it’s awesome, let’s just get that out of the way), but when I open it and play, I can’t figure out how to do anything outside of the nexuiz application, let alone, actually quit the game, except by using option/command/delete to force quit, which i’m sure i shouldn’t have to.

also, I see those pc controllers with joysticks that look like console controllers, can you use them on any game, or just certain ones?