Within your organization, go to the 'Collaborators' tab, then click ‘Invite Collaborator’ to invite users to your Organization. An invited user who has yet to create an account is shown by the role of ‘Invite Sent’.
From there, enter a name, email, and choose project and access levels. Learn more about roles and access level permissions.
Once the user is added, they will receive an email with a link allowing them to create an account.