The Multi-Admin Addon gives you the ability to specify additional Admin Users which allows them to have access to your software's Admin Control Panel.
This is done by first creating one or more Admin Groups. Each Admin Group will have its own permissions settings, which include access to view and/or edit certain sections/pages of the software's admin panel.
Once an Admin Group is created you can then assign any current registered user in the system as an Admin User. After a user is assigned to a User Group, you can then also specify certain access rights specifically for that user.
Note this feature does not create admin users within the system. It only assigns administrative rights to currently existing users.
See Addons > Multi-Admin > Admin Groups for help with setting up the multi-admin addon for the first time.