A .torrent extension file contains all the information needed to download the file for which the torrent was created like file-name, its size etc.
U torrent is an application s/w for downloading files associated with their respective torrent files.
This application s/w is based upon some proprietary application layer protocol for p2p (peer-to-peer) file sharing.
Roughly speaking in p2p file sharing one end user, called peer, downloads files directly from another end user(s), called peer(s) without involvement of any third party server.
One can create a .torrent file out of any file and share it. Seeder-a peer who provides the file to be downloaded for which the torrent has been created. Leecher-a peer who d/ls the file. Once a peer has d/led the file, it can become seeder. So, you become server when you provide the file and client when you download.
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I think this much solves your purpose.
So Cheers!