1. Admin CP --> Users & Groups
2. Left Menu: Groups
3. Add New User Group
4. Name Group & Set Permissions
After you have your new group created, make sure they have the appropriate permissions in EACH of your forums.
1. Admin CP --> Forums & Posts
2. Select Appropriate Forum
3. "Permissions"
I would map out a basic idea of what permissions you want for each group "level" and then make "Registered" users as the most basic/limited of those permissions. Then, when you create each group you can "copy" the permissions of the previous group and just add in the extra permissions you want.
For example, if you start with "Registered" as your "base" and you are absolutely certain those are the permissions you want, then just create a new group based upon those permissions. All you have to do then is add the extra permissions for "New Group". Once you have "New Group" completed (with forum permissions set etc.), then create "New Group 2" based upon "New Group" and all you have to do is add the permissions that "New Group" & "Registered" do not have.
This helps you stay consistent and it eliminates the need to reinvent the wheel every time you create a new group. Take notes so when you decide to add another group three weeks from now, you will remember how you set everything up. Hehe.
All the best!
-- ETA --
After you are finished with the group & forum permissions, then go in and set your group "promotion" settings. Make it too easy and it will "cheapen" the rewards, make it too difficult and your users will be frustrated. Finding the balance between the two is the challenge.