There are groups as you at the bottom of the screen, and this how you join them or rank up.
New Members - Initial starting, new Forum members will auto-subscribe and accepted here on signup.
Members - Once you made 10 posts on the forums, you will be auto-subscribe and accepted here.
Moderators - Only way to join here if you're accepted into the position of a moderator. Just remember, your game ranks won't matter here to much. As chat moderation is extra work required on being active on both the game and forums. Trusted members will be requested to take on the role of a moderator when the forums become larger.
I will edit this post when more user-groups are added. So if you nee new groups, please refer to this posts on what it is about.