What is a torrent software?
Simply you can say that BitTorrent is a software to download files.
How to use torrent ?
Bittorrent is a software which accepts file with .torrent extension. So if you want to download any file or film or any software, first you should have a torrent software to start download (you can download a torrent software from here it is free), then you need a torrent file (with .torrent extension).
you can download the torrent of that file or software from any indexer website of torrents. A indexer website is a website that compiles a list of torrents.
Then you can start download your file by double clicking on .torrent file.
Note: Be sure that the file you are going to download is not pirated. piracy is a crime in many countries.