Hi there =)
If you go into your User CP, look down on the left hand column for where it says "Group Memberships", and you'll find a list of private groups. Many are for specific religions only, so if you aren't that religion, you shouldn't join that group (we do have a Pagan Group though, so you may want to check that out). Also, the Rainbow Alliance group is for GLBT members, and our straight members who support the GLBT community.
The Eros room in particular has more rules, and we ask that members not join that group until they've been a member for at least 9 days, and be 18 or older.
There is also a group for theists, and one for non-theists. However, you can only join one