Ok, well BitTorrent or any other Torrent Bassed Client uses Advanced Packet Technology along with Trackers through TCP/IP Handshaking Protocols which send & receive all the bits (0 / 1) needed to complete the File on your FAT32/NTFS based HDD, through various Internet and Intranet Gateways, routed through your modem and ISP from one Peer (You) and another Peer(s) (Somebody else). Your Local client seeds all the necessary bits needed based on advanced algorithms which are monitored for the scarcity of the file in question when upon completion of the packets already received, on your side. When you do not seed, and download more than you can chew, you are considered a leacher.
hope that clears it all up.
bwhahahaha!