Homebrew,quake and halo on psp?

ok, i just got my psp slim, and i want to play halo on it. i heard there is a game quake for it, and there is a new mod that came out that lets u play halo style or something, it says its homebrew, so i was wondering how to put or make homebrew run on my psp. please answer ASAP!! make it as easy as possible to understand