All menu links are published by default.  If you do not want users to navigate to a certain page, you can accomplish this by unpublishing the menu link.  This will not delete the menu link or the static content page.  Users can still access the page if they have the correct URL, but pages (Articles) can be unpublished as well.

1. Login to Joomla
2. Hover over Menus
3. Click Main Menu (some sites will have multiple menus, they will always be listed in the Menus area)
4. Click the 'Check Mark' icon next to the menu item you wish to unpublish
5. To publish a menu item, simply click the 'Red X' icon

Note:  You can perform the same task by checking the box next the the menu item and clicking the Publish or Unpublish icons in the upper right menu