Group access with user on it upon register

Hello,

Normaly, all user will see the website as regular… but some pages and post,

What I want is that : able to create several groups and anyone can register to create an account by selecting on the group they want to be.

Once I apporve (admin), they can login and see the pages and post associated with that group

I would like to know how can I create that

I did some research before creating a post any guide will appreciated

Bye