BitTorrent Confusion

Can somebody explain BitTorrent to me? I could go look it up for myself, sure, but it’s easier just to complain here. I know basically how it works, but what’s with the queuing system? I’ve had two files sitting in Azureus for three hours now and they haven’t started downloading yet. I know they will do at some point. Is it something to do with how many files I have seeding?