In the Pages section at the top of the Design Center's Control Panel, you will see all the pages you've created for the site opened. Clicking on a page name will load that page into the Canvas on the right. It will also make available four functions for that page:
To reorder your pages, click the Reorder Pages button at the top of the Pages section, and use the arrow controls to move pages to the order desired.
To add a page to your site, click the Add Page button in the Pages section, enter a name for the page, and select a page layout. Then click the Add Page button at the bottom. This will display the new page in the Canvas on the right. Your pages can each have a different page layout.