The page name is the text for the link that will be displayed in the website's navigation menu. In the "Edit Subpage" tab under the "Page name:" area enter the name that you would like and then click the "Save Changes" button. You can edit this at any time and it will automatically update with the navigation menu.
*Note: Pages which are not currently being displayed will not be listed in the navigation menu of the website, though you will still see the page listed in the menu of the admin section.