User management is done partly outside Drupal. When you assign permissions, we are talking about roles. Those roles can be defined as an existing user or an e-group. We recommend using e-groups because adding and deleting members from a role becomes easier. All the e-groups management is done in e-groups application.
If you need to add more roles it's convinient to call them all starting with drupal-admins-<sitename>-web-cern-ch-<egroupname>, so you see at a glance all the related groups to a site.