You may change a page's privacy level from the All Pages overview page or the edit page view.
All Pages Overview
Edit Page View
Each page can be set to one of three levels of privacy/visibility: on, off, or private. Pages that are On are visible to all site visitors. Pages that are marked Off will be hidden, and is akin to a draft or unpublished status. Pages that are marked Private are visible only by direct URL. Private pages will be excluded from your page menu.