you need a torrent "client" - the torrent file itself is just a link to a tracker and once you start the file running it connects and you efffectively pick up the file from in bits from "seeders" - whilst downloading you are a "leecher"
Worth googling for some programmes (they should be free) have a look under Bittirrent or torrent client for example
(I use a very basic programme called BURST, looks like an old MSdos interface but does the job well.heres a useful site
http://www.dessent.net/btfaq/