I just downloaded and installed BitTorrent and the only other p2p sharing program I have used before was Kazaa. How exactly do you download stuff via Bittorrent?
Ok, first you need to get .torrent files. To find .torrent files try www.torrentz.com.
Find a .torrent file of what you want and make sure it has a lot of seeds (people with complete copies.). You download the .torrent file, you should make a folder somewhere to keep all of them. Then you open .torrent file in BC and pick a download place, either default or a specific place and it will start downloading the file. 
For configureing BitComet try this set up guide, its not the best but the author tires his best (j/k BD 
) Guide