User Managers are Managers that can manage all of a user's enrolled courses and not just the courses that are assigned to their groups.
To create a Manager, you will need to first create a group and add the users you want the Manager to be able to oversee, then assign a Manager to the group. Next, edit the permissions of the Manager so that it looks like this:
* Only the last option is mandatory. If you only want them to be able to run reports on the users and not be able to edit their progress, do not check the third option.