MAM is myanonamouse which is a private tracker focusing on books and audiobooks. It is generally seen as one of the easier trackers to both get into and maintain your ratios on and is a good place to learn how private trackers work.
From there it helps you get into others by having a proven track record as well as being able to get invites via the MAM forum sometimes from other users etc.
I love the place as a lot of what I get is audiobooks anyway, it is super friendly and people will help you out as long as you have done your due diligence and aren't asking stupid questions that are covered in their already extensive documentation and forum.
Thanks. Gonna check this out :)