Here is an example image of "Group membership" with 2 accounts. There's only one user in the list, named Tiago. That's because Tiago's account is without Administrator rights.
Permissions shown below are only visible to the users with Administrator accounts. Administrators are never listed because they have complete control over data and users in Group.
Permissions are divided by Data type (image below).
Here as an Administrator you can specify exactly what users can do:
1 - Read (View/See data)
2 - Insert (Create new data)
3 - Update (Edit existing data)
4 - Delete. (Delete data)