At the top you see all current pages and below the links in your main and top menu
You can move your menu items around by first clicking on one and then moving it by using the arrows
You can create a submenu by moving an item under another one
You can add an existing page to a menu. Click on the page you want to add and then To Main or To Top (under Website Pages at the top) depending where you want to add it to.
You can also add an existing page by clicking on Add Link and choosing the path to the page from the list.
If you want to add a menu link to a new page that does not exist yet you have to add the page first.
You can add external links (links leaving your website to another website) by clicking Add Link. Choose External Link from the Link To section and then enter the URL in the http:// field.