It's nothing like DIS.
Do you know how to use Torrents? If not, try and find a good step by step tutorial online. I use Azureus. A quick google search will get you a link to download the program. If you ever used any peer to peer programs (the old Napster, Limewire, etc) then it should look vaguely familiar when you run the program. It's the same idea, except instead of searching through the program, people set up websites where you can download a small file that will tell the program where to find the file. . .then you download from other users.
So once you have a program up and running, register at mousebits.com - that's the only way to get into the sections to download. Once you find something you want to download, click the link and choose open - it'll then open the file in the program you're using. You'll most likely have to confirm (I have to choose OK on Azureus). If you choose save instead of open, no big deal - just double click on the file that downloads. Remember, the file you're opening from Mousebits it just the path to the file, not the file itself.
There's a forum over there for some general discussion, discussion about the files available, and techy stuff. But it's not like here. There are a lot of really nice and helpful people on the forums, but it's not like the DIS where there's a ton of travel planning and sharing life stories. It stays fairly to the point with torrent specific discussion and some park news.
One thing to note - it's a relatively small site (compared to the big Torrent sites like piratebay) so a lot of times you'll find files that have no seeders. Especially if you're trying to download a file that was uploaded a good while ago. If you really want the file and can't get a seed, just ask and people are usually pretty helpful with getting it available to you.