The pages http://en.support.wordpress.com/pages/ we bloggers create are static and cannot automatically update. Only the dynamic categories pages created by the software will automatically update.
Though there is only one dynamic page in a blog for posts and we cannot post to more than that one page, we can create the appearance that we have posted to more than one page. We organize posts by assigning categories to them. You can create a custom menu and add the dynamic categories pages into the custom menu.
Here’s a link to a custom menu walk-through > http://onecoolsitebloggingtips.com/2011/08/11/wordpress-com-custom-menu-walk-through/
There are many common errors, misunderstandings and misconceptions when creating custom menus and you can read about them here > http://wpbtips.wordpress.com/2011/12/19/custom-menus/