It's a .torrent file?
Well that means you haven't downloaded it yet.
You're going to want to install a torrent client to open that file & to actually download the game.
Since you're not an experienced torrenter & probably wont become one, I'd maybe recommend "Deludge", very quick, basic and easy to understand. And it's ad-free as well.
After you have the torrent client installed, you should be able to just double click your .torrent file and start downloading it. (Assuming it's not a dead torrent (if it is, you won't be able to download it))