Simply go to the staff are > select a staff you would like to make 'manager' > scroll down to the 'role' section > using the drop down, select the staff tha you would like this manager to manage > save changes
After this point, when this manager logs in, they will see their own profile and appointments as well as the profiles and appointments of the staff that they manage.
This role will be able to adjust all the settings of the staff that they manage and reassign appointments of those staff too.