Visit Pre Social and select Applications > Groups. On the right, you'll see a link to "Create". Enter the name of your group and a short description. Click save.

That's it, now you'll have the option to edit your groups avatar. Click on 'Invite Friends' and you can send a message to your friends to join your new group.

Trying to drum up members? Put a link to your group in your forum signature.

Since we're talking groups, if you are a Twitter user, join my Twitter Users group.