Customer accounts are organizational units (think of a business or a hospital) and each account will have a set of users (think of employees) that will have specific privileges based on their role within the organization. From this tab, users are able to see a list of other users within the customer account.
An address book for interaction with others that are not in the same customer group. For instance, let say that Mark Sloan needed Frank Steveson -- a user from another customer account -- to review a document before submitting, then Mark would need to add Frank to his list of contacts.
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