The 'Users' app that was introduced in Shock OS 5.0 Eddie is now broken in this release. This app does not appear in the start menu and launching it from the terminal will result an error. THIS WILL BE FIXED IN THE NEXT RELEASE
For now, the following steps will help you manually create additional users:
Open a terminal and enter the following command:
$ sudo adduser [USERNAME]
Replace [USERNAME] with the desired name for the new user. You will then be prompted to create a password and fill out other information, such as the full name, for the user. Once you have finished, execute the following command:
$ sudo usermod -a -G adm,dialout,cdrom,sudo,audio,video,plugdev,games,users,input,render,netdev,spi,i2c,gpio [USERNAME]
Replace [USERNAME] with the username of the user you created in the previous step. This command grants "normal" user permissions so the user can actually use the system.
And that's it! Shock OS 7.0 Garrett will include a properly working GUI user manager, but for now this should work.