The person who establishes the Corporate Contacts Account is automatically made an Admin User. This type of user can purchase, upgrade and downgrade packages, check error logs, see the system status and add new users (including Admin Users).
A standard User is able to perform all of the usual Corporate Contacts functions relating to Folders, Connections, Contacts and Appointments. However, they cannot access the financial and system maintenance of the account. In general you would expect most additional users to be this type.