Yeah, each model is a number which are believed to be in the order of which they were created from. There are originally Twelve humanoid Cylon models to conspire with the Twelve Colonies, although we only know of seven. This season they're finally getting to the question of where the final five Cylons are. This is, of course, to answer the question of whether Gaius is on of those final five or not.

It's okay, as I mentioned it is a very complex show and not everyone can get drawn into it that easily. Surprisingly though, I just got addicted to it not too long ago myself, however I understand everything they're talking about. Perhaps it clicked with me from the beginning since I was already intrigued, partially due to it's political and religious based premise of morality. Heh.