If you are to manage a lot of users, it might be a good idea to organize them in separate groups. To do so select "new user group".

Enter the user group name and, optional, a description of the group. Then save the user group.

To add users to a group, edit a user group, and click on "add members". Select the users to be added to the group, and click "Ok". On the user group page you will see all the users listed.