A user is called a person in innius. Use the "Invite" button on the "Persons" tab in the administration web app to extend an invitation.
The person should have the same email domain as that of the company, because that is how innius uniquely identifies a company. For instance, if the company "XYZ" is initially created with user1@XYZ.com, then all persons in that company must have "XYZ.com" as their email domain.
The invited person receives an email with a link to register login credentials in innius. After replying to a confirmation email, the new person is up and running in innius.
Persons belonging to other companies cannot be added. They can gain access to shared data by setting up a trusted company relation first.