Tasha, chapter 3 of "Easy Game" has a pretty good introduction on fold equity and how it can be practically applied to game situations, as well as a detail of what factors it primarily depends on. The posts above are spot on, obviously, but if you'd like to be properly acquainted to the topic I suggest reading it.

I may or may not have .pdfs of this book, which I may or may not give you if you decided to log in to IRC with us.... hint hint