While it is possible to change permissions on a per user basis, it is strongly recommended you use Groups instead. Just as for users, there are "Backend user groups" and "Frontend user groups".
This chapter provides a quick overview of backend user groups. In the next chapter we will look at changing user permissions using groups.
Backend groups can also be viewed using SYSTEM > Backend users module:
We can see two groups that correspond to our users ("simple" and "advanced").
To find out what group each user is a member of, select the "information" action icon. A pop-up will open with detailed information about the group. Scroll down until you find the "References to this item:" section. This shows the list of backend users who are part of this group.