Bittorrent is a protocol that lets you download files from other users. It's all about sharing. Seeders have the files and are distributing them, leechers are the ones who download. Once you download a file and have 100% of it, you can become (and should become for the community) a seeder yourself.
The files are downloaded using a client such as uTorrent or Azureus/Vuze. You must first download or open a .torrent file in order to tell your client how to download the files that you ultimately want. Trackers (public and private) find and manage these .torrent files, and also keep track of seeders and leechers.
That's where Bit Che comes in, it can search a variety of public trackers for a tons of .torrents, depending on what you're looking for. Then you can download the files using your client of choice such as uTorrent or Vuze like I mentioned before. If you want access to private trackers, which usually have a better variety of files, you'll need to sign up or in most cases, be invited to sign up by someone you know already in the tracker.
I hope this explains the process well enough for you. Let us know if you have any specific questions.
