Torrents work differently than direct downloads. When you download a torrent, you’re not downloading from a site, you’re downloading from other people who’ve downloaded the file (these are “seeders” and the downloaders are “leechers”). As you download, you’re also uploading the parts you’ve downloaded to other leechers. Once you’ve finished downloading, you become a seeder. The more seeders there are, the faster a leecher can get the files, because they can download different chunks of the file from different seeders simultaneously.
The problem with public trackers (like Pirate Bay) is that most people don’t seed. They download the file, then delete the torrent - known as “hitting and running.” This means over time, it’s harder to download the file, as the number of leechers outweighs the number of seeders. Once the last seeder deletes the torrent file, the torrent is dead.
Both MySpleen and Blutopia are trackers you have to be invited to. MySpleen no longer accepts new members at all, invites are disabled. Blutopia gives you “credits” for uploading, and to invite someone you have to cash in some credits. (I think. I haven’t checked into that.)
As for the rules once you’re in, MySpleen requires that you keep your upload/download ratio at a certain level (typically at least 1.0, which means you’ve uploaded as much as you’ve downloaded). In theory, you can get to 1.0 while you’re downloading and never actually seed the completed file.
Blutopia not only has this requirement, they also require that when you download a torrent, you seed it for a full 7 days, regardless of what your ratio is on that download (so if you get to 1.0 after 2 days, you still have to keep seeding for 5 more days). This prevents hit and runs and keeps torrents healthier longer.
Hope that clears some things up. I’m typing this at work so I may have skipped some things.