Well, the user groups Administrators and Global Moderators are already there by default.
So is the Registered Users group and the Newly Registered Users group. You can apply all sorts of Permissions
to these groups.
That only leaves the Power Users group. You can of course create the group in your ACP -> Users & Groups -> Manage Groups and start assigning permissions to it. But I have no idea what a Power User is and how you'd get to be in the group.