Roles define what privileges a member has.
Guest Guests can view Private Data on your site. However they cannot make any changes to your site.
Member Like Guests, Members can view Private Data on your site. They can add or update only their direct relatives (parents,children,siblings and spouse).
Administrator Administrators can view Private Data on your site. They have limited ability to make changes. They can add/edit/delete any names and pictures but cannot make any other changes.
Cheers
Paul