What exactly don't you understand?
Bittorrent is to upload and download massive files. (I've accessed entire seasons of "A Bit of Fry & Laurie" that way, since it's not available in the US.) and I believe a number of non-US people on the boards here access their new "House" episodes the same way.
The wikipedia explanation is here:
http://en.wikipedia.org/wiki/Bit_torrentYou typically also have to have Divx downloaded on your system to actually play the file.