You can invite users to your CMS to collaborate with them. Inviting someone is a matter of having them sent an email via your CMS settings on your Scrivito dashboard (click the “Users” tab after selecting the CMS concerned). The email sent includes a link for accepting the invitation.
Each CMS user can be assigned one of several roles, e.g. “Chief Editor”, to specify the actions the user is permitted or denied to perform (e.g. publish working copies). Only the users of a specific CMS are permitted to access and use the editing interface of that CMS (in accordance with the respective role you gave them). Neither users of other Scrivito CMSs nor visitors can open the editing interface of a CMS unless they have been invited and have accepted the invitation.
After a new user has accepted the invitation, you can share your working copies with them.