Need help downloading on a mac!!!

Hello,
I already have the sims 3 base game on a disc and a few other eps that I bought myself. But I would like to download other ones including Seasons and Pets. 
I go into the games4theworlds downloads list , and I click The Sims 3 Seasons which brings me onto another page and it downloads but when it downloads it is a torrent file. What do I do about this?  I already have Stuffit Expander installed also. Thanks

I'm no expert on here but I think what you need is a torrent client, which is needed to download torrent files. Download a torrent client such as utorrent and then try your download again.

Indeed, you'll need a torrent client such as uTorrent or Transmission.
After you install one, you can drag and drop your torrent file to your torrent client and the download will proceed

Here is a guide from G4W about torrent and how it works : http://games4theworlddownloads.org/Downloads/Guides/How_to_download_a_torrent_Guide.pdf