Well, but what it that is meant by metaphysics? I've heard the word many times, seen its use, and I still don't know what I'm supposed to do with it.

It's a bit confusing in part because of its strange etymology. Originally, "meta" was used in the sense of "after", since "metaphysics" was the unnamed book that came after "physics" in the standard ordering of Aristotle's works. Later scholars accidentally connected that to something like our current usage of "meta", and a somewhat arbitrary field was born.