BitTorrent is a peer-to-peer file sharing protocol used for distributing large amounts of data. BitTorrent is one of the most common protocols for transferring large files.
For downloading torrent first you need a bittorrent client, such as uTorrent.
Install uTorrent and start browsing internet for your desired content, find and download .torrent file, than open .torrent file with uTorrent and start downloading the content.
Any .torrent file is a small file which contains information about the data you are interested to download.
Bittorrent client use .torrent file to connect to trackers and download those content.
Any seed is a client that offers a full copy of the data of a certain torrent. When your BitTorrent client finishes downloading, it will stay open until you close it. This process is called a seed or seeding.
Any leecher is a client that is currently downloading a torrent. The only one thing that differentiates a leecher from a seed, the first one does not have the complete file.
A tracker is any server on the internet whose main goal is to coordinate the actions of BitTorrent clients. Every time you open a torrent, your computer connects to the tracker and asks for a list of seeds and leechers to contact to.