Can't add much more to what yAd519 has said.
Your level of membership is based on the number of posts you have.
Moderators and Super Moderators are appointed by the Admin. They watch what is going on in the forum and take action as necessary when someone is out of line.
Did a search of the FAQs
What Are Moderators?
Moderators oversee specific forums. They generally have the ability to edit and delete posts, move threads, and perform other manipulations. Becoming a moderator for a specific forum is usually rewarded to users who are particularly helpful and knowledgeable in the subject of the forum they are moderating.