Torrents is based on sharing ("Filesharing"). You can just download, what other peoples are uploading.
"Seeder" are the ones who got the file at 100%
"Leecher" are the ones who are downloading
While you download, you are uploading too (Sharing, remember?)
On that way you can get high-speed downloads without a stand-alone server and you are savin bandwith of the one who offers that file basically. Freeware or Linux for example are using torrent to save theyr bandwith.
On sites like
www.mininova.com (english) or
www.bitreactor.to (german, but a lot files are english) you can search and townload files with the extension *.torrent
If you open this file using a torrent-client like Azureus Vuze,