If you are member of a group equipped with additional admin rights (find out more in rights) you may create a new group user. Go to the member area and select the desired group for which a new user should be created. Then select create new user under the menu point what can I do here in the content menu on the right side of the screen:

This will take you to following page:

Enter the new user’s user name, first name, last name and e-mail address in the according fields and confirm by clicking create user. The new user automatically receives an e-mail notification with his user name and a generated password. The new user is automatically member of that group.