Private Trackers are solid options if you're looking for some data in a specific niche that public trackers don't offer quite well. Their signups are controlled by admins which makes harder for media companies to go in and send cease letters to torrenters. This does not mean they can't however.

On a public tracker, anyone can be part of the seeding chain without any authentication; meaning they can monitor who's torrenting what pretty easily. However for each private tracker, there has to be a seperate infiltration. Combining limited signups and being invite only makes hunting for them difficult.

To find them, you're gonna either look at tracker forums' open signup threads as a beginner; or if you know people that could have access to these trackers ask them for invite. Most private trackers have strict seeding rules, so seed them according to their rules.