Creating a Torrent File is renowned for being a hard and tedious task. However it is much simpler than most claim to be.
Step one: open up your preferred torrent client.
Step two: click file > New Torrent
Step three: Follow the procedure, select the file you want to covert and what yo want to call it etc...
Step four: Click Create Torrent.
Optional: You can also choose to seed your file at this point. This will increase the speed at which people will be able to download your torrent.
And there you have it, your very own torrent file. You can do whatever you want with it; Just keep it, or even upload it to a torrent website.