When adding users to your workspace, they are going to need both the Workspace ID and the Registration Code for the workspace you would like them to register for. These can be found by navigating to the Workspace page [1], pressing the People tab [2], and then pressing Invite Users [3].
The Invite users button will bring up a window containing the workspace ID and registration code your new user will need to register.
New users can follow the steps in the guide: How do I register for Go TCMPC?