As you can see by the answers your questions isn't all that clear. An admin in a group is promoted by the group owner and is a regular CafeMom member.
The CafeMom Admin Or CafeMom GroupAdmin OR CafeMom Team or similar names are CM employee teams who have the job of overseeing activity on the site. Cafe Amber or similar people are specific CM employees who are a part of those teams. Short of getting a job with CM regular members don't get to be a part of that.
a group owner usually invites you, or you ask .. and they determine it by your answers, your time spent in the group and our your friendships.. i guess there are other reasons also like how knowledgable you are about the group subject, or objectives or how popular you are on the group.
Do you mean as a whole as part of the cafemom team that runs the show? I would think you would have to contact Cafemoms about that one otherwise if you want to be a group admin see if any of the groups you are in need help.