Only Administrator users can access this section.
For accessing User Management dialog click Preferences button at top left-top corner of 3dCutout window.
Each user in 3dCutout has its position and permissions. Each user that creates workgroup will be Administrator. Administrator is free to access all section of 3dCutout.
In this section you can see (Windows) users. If a user name is not in this list just add it manually.
In this section you can tell if user is Administrator or not.
Each user can have different permissions and positions in different projects. For example a user can be Animator in a project but Rig man in other project. So first select desired project before setting permissions up.