Under Settings (bottom left)/Users/Invite new User, a new user can be invited to your license and their access rights can be managed.
First you have to enter the E-Mail of the new user. Afterwards you have to choose the role.
Admin: Admins have the same rights for the selected areas as the owners of a license. So they can also manage the license and for example add new users.
User: A user can only access the areas that are assigned to him. However, users have no rights to manage the license or change settings.
Access is regulated by a check box in the according field.
Access to specific projects can be authorized here.