Any user can create groups. Org Admins and Group Admins can add/remove apps and users to/from a group. The user who creates a group becomes the Group Admin for that group. Org Admins and Group Admins can change Group Admin permissions of Users, including their own.
Group Admins can only administer those groups for which they have admin permissions. Org Admins can manage all Groups, even if they haven’t been explicitly granted Group Admin permissions.
The platform uses groups to manage pipeline access to layers, which means that apps can only write to output layers if they are part of a group.
Only Org and Group admins can change User permissions. Org Admins can change User permissions on any Group. Group Admins are restricted to change Users permissions for only those groups for which they have admin permissions.
Only Users can be Admins. You cannot make an App an Admin.