basicly you start out as a human, and defeat NPC hollows until you either die or commit suicide. From that point you turn into a spirit. If you go to the seritei, and train you can turn into a shinigami. if you get eaten by a hollow you turn into a hollow, and eventually you can become an arrancar. as a shinigami, you can join a fraction, (im in 6) and continue to kick hollow ass. there is a full forum that goes alongside this site.
you can become a bount, but as of this point im not sure how...
any other questions?