There are two types of Managers/Supervisors you can build in the system.
This one walks through Organization Managers/Supervisors which allows you to assign an employee to oversee a department or group. If you add an employee to that same group, this employee will automatically have access to view them as a manager or supervisor.
The other option is Assigned Managers and Supervisors which gives you a change to assign managers and supervisors to employees 1:1