In the "Add to Menu" section you will decide which menu you would like to add your page to from the drop down menu.
*Note: By default there is only one menu but you do have the option of adding more menus from the "Menu Options" section in your admin page.
*Tip: Not sure why you would have more than one menu? The menu option allows you to switch your whole menu to a new menu with just a click of your mouse. This comes in handy if you like to switch your menu for the holidays or if you are creating new or better pages that what you already have you can save them to a different menu, test them, and if you need to make more changes or you decide that you like what you had better you can switch back to your old menu. A second menu also provides a way to keep track of which pages are currently being displayed. You can keep the active pages in the main menu and put the inactive pages in a secondary menu. Only one menu can be used at a time.