First, some info on what bittorrents actually are: BitTorrent (protocol) - Wikipedia, the free encyclopedia
You need two things:
1. A bittorrent client, I personally use the official client, but there are others, and its really a preference. Stay away from bitcomet though, bad bad joo joo.
2. A website to get torrents off of that have the stuff you're looking for. Up until this point, bittorrents are legal, as its just a means of transferring files between computers efficiently. Its the stuff you're transfering that is questionable (IE Piracy). I will not give, nor should you ask for a torrent site on AO. This is where you have to go out on your own and find a torrent site for you to use, trust me, there's a lot of them out there.