I really don't understand Christianity?

I am an ardent atheist (just to clear the air haha). And i was talking to a few christians in the own where I live about christianity and about what they believe, about the trinity, and the existence of god, and a lot of their arguments seemed to be mired in words and terms. Now they seemed pretty stupid people anyway, (they said if you go to areas where there is more catholicism, there is more crime; and that ity didn't exist before the 50s) so can someone explain to me properly the concept of the trinity, of where Adam and Eve fit into it all, and how your sure it's your god up there? I don't mean offense, but there must be a coherent view that I just ain't getting.