You can only add new user accounts into an internal user domain. 


On the DualShield Administration Console, you need to go to Directory>Users  

Or you can click on Shortcuts>Manage Users



                  





Next select your new domain from the domain dropdown, at the top


Click on Click on Search



                  





To create a new user account, click on the Create button on the top right.



                  





Complete the details as needed for the user account

and hit Save