A user can be a guest or a host. Their details are added on the Edit My Account page in the frontend. Just how much information on this page is visible depends on who is viewing it. If it's the user, then all information is visible. If it's a manager of a property that the guest has made a booking on, then they can see all of the private data, as can Super Property Managers. Everybody else can see just the publicly available details, and reviews that they have left.