I was just wondering how people become these ranks . . .
Admins are staff members - so get a job with Duolingo. https://www.duolingo.com/jobs
Moderators are invited - often because they are course contributors, but also just general behaviour in the forums. https://support.duolingo.com/hc/en-us/articles/204980530-Who-are-the-forum-moderators
And before you ask ... course contributors are invited, usually after they fill in the application form in the Incubator. http://incubator.duolingo.com/apply
Q. How to become a Duolingo forum moderator?