Mmmm I'll do my best. The client I use is uTorrent (like the sign for nanometer, not just a plain u at the beginning). Others swear by Bitlord.
First you need to download and install (I guess, on a Mac) a BitTorrent client program like the ones I've listed above. If you go to
www.torrentpond.com you can click on the link for uTorrent and then download the executable only. That's a neat way of doing it... no mess and no spyware.
Next, use a search portal for torrents like TorrentPond to look for what you want. Use the radio buttons on the left after searching the first site by default when you click Search if the first site doesn't come up with anything.
When you get results (good or bad), on most torrent sites there'll be a "torrent health" bar. That means that currently, there are either enough people online for you to get a complete copy of the file(s). Green (or a complete green bar) means at least one full copy's worth of pieces are online. Anything less and you can start on it, but there's no guarantee you'll finish it any time soon.
Once you find a torrent you want, click the first link for the file... it'll take you to a page with a link to the .torrent file and some more info about the torrent itself (most of the time). Just click the .torrent link and save it to your HD, somewhere where you'll remember where it is.
Once that's done, launch the BT program you've chosen. Go into the settings (and if required, advanced settings) and select 0 for available upload slots if you're using uTorrent. Otherwise, you may need to poke around some. The reason I tell you to do that is otherwise, depending on your provider and what you're downloading... you could be "warned" for illegal sharing of files. They're also in the middle of changing copyright laws right now in Canada, so it's best to watch your ass.
There'll be an Add Torrent under the File drop-down menu. Pick your Torrent file you saved earlier, then pick a destination for the completed files to go. You'll see there are Download slots (normally at the top half of the screen) and Upload slots. Current downloads go in the obvious place and detail their progress (download speed, number of peers you're connected to, percentage complete, etc.). Current uploads appear in the lower half of the screen.
I tend to have my Torrents folder for all the .torrent files and then a [FINISHED] subfolder for the completed items. The square bracketing allows the folder to stay as the first folder in your Torrents folder. I say that because when you're downloading torrents, they tend to make their own temporary folders under your main Torrents folder.
Once your torrent is complete, your Torrent client will likely perform a checksum operation against the files you've downloaded, check for consistency and it may even re-download chunks it needs to replace bad ones.
Once it's done, most clients move the completed torrent to your uploads slots. In uTorrent, you can right-click it and Remove the torrent and Delete the .torrent file. Because it's done at that point, that's what I normally do.
So, everything I've told you is operationally correct. You might want to Google "Mac BT client" or "Mac BitTorrent client" if uTorrent won't run on a Mac.