1) Click on the user avatar in the upper right corner and then click on Users
2) Click on your department group on the left
3) Click on "New user
4) Enter user name (e.g. last name) and e-mail address. The field "Add user to group" should be prefilled with your subject. If not, select manually again.
5) Click on the checkmark. The new user will now receive an email with the request to assign a password.