Pages vs Posts http://en.support.wordpress.com/post-vs-page/
1. You create a custom menu. http://en.support.wordpress.com/menus/
2. You add the Parent pages you want to display and arrange them in the order you want.
3. Then you add and drop and drag the subpages below the appropriate Parent pages, and when you have everything arranged in the menu that you want you save the menu.
4. Go to the “theme location” module at upper left on the menu page. Select your custom menu name from the pulldown labeled “primary location.” Click the save button in that module.
5. Refresh your browser so that it isn’t possibly pulling a cached page, and view see your new menu with Parent pages and dropdowns to sub-pages.
Troubleshooting – My pages are in the wrong order
Check the sub-pages themselves to see if you have established a Parent page and child page “hierarchical structure” in the page attributes module. Remove if required. Also remove any “order” numbers you have assigned that may conflict with the order you are creating by dropping and dragging. Or simply change them so they are the same order as you establish in the menu. Establish consistency – problem solved.
Troubleshooting – My Pages aren’t appearing
They must be public pages – not private.
Public – The page will be visible to everyone.
Protected – The page is protected with a password you set. Only people who have the password can view a protected page.
Private – Pages are only visible to blog Editors and Administrators. Private pages are not visible in Blog Surfer, feeds, or in any search. A page can be private without being password protected.