Use the following settings when adding a menu item via the "Menu Settings" section.
1) In the "Title" field, enter the text of the menu item
2) The "Description" field may be left blank, or can include additional information to be displayed when the user's cursor hovers over the menu item.
3) The "Parent item" field determines where on the menu the item will be displayed. For main menu items, the parent should be set to "Primary Links". If the parent item is set to an existing menu item, the new menu item will be displayed as part of a submenu.
4) The "Weight" field determines how far down on the menu the item will appear. If the weight is set to zero for all menu items, they will appear in alphabetical order. Otherwise, select a lower weight to make the item appear higher on the menu or a higher weight to make it appear lower on the menu.