Server which is a tracker here in this P2P network the server will have a torrent file with extension .torrent this file consists of tracker that where are the files are shared and from which IP/Machine it is published/shared all the information about the files will be tracked by server.
Here Server act as an intermediate to all the Machines Server does not contains any files it will have only trackers inside the .torrent file.
Seeders : Seeders are normally known as publishers when ever a file is published with the help of torrent server the publisher is the first seeder.
Leechers : when others download with the help of Seeder (Publisher) they are know as leechers
If the leecher downloads fully automatically the software starts to seed to others this is optional in some softwares. But without seeders you cannot download files as fast you can more seeders more fastly you can download. So before Downloading any torrent file you should check how much seeders and leechers are there and start download the torrent file.
Here is an screen shot while downloading a file using utorrent software .
Main Tamil Torrent sites
www.tamiltorrents.com (Tamil) Forum (have to register and pay for downloading as a new user)
www.tamilthunder.com(Tamil) Uses Forum, To download .torrent file you need to register via forums and download the torrent file from the forum posts.
www.tamilmixer.com(Tamil) Need to register and can download via browse
Famous Torrents sites
www.torrentz.com Torrent Search Engine.
Note that 90% of the torrent sites are to be illegal while you download any file from torrents it is under your risk