Users can be added to the Active Extranet Users system group (grey) via the user data. If you are using the Advanced spreadsheet to import user data, the Type column allows you to determine if someone is an intranet or extranet user. If user data is being imported from somewhere else, we recommend reaching out to your Account Manager to ensure everything is set up correctly.
Alternatively, you may prefer to manually create a user group (red group) for Extranet users. To add a new group and view existing, you must be assigned as a User and Group Manager. Go to Action > Configure > Manage Groups.