Your site’s top horizontal navigation is automatically generated from the hierarchy and order of the folders within the Site content menu. This type of navigation is called dynamic navigation because it’s automatically generated and updated.
This menu only picks up folders/directories but can be forced to display specific pages in the root folder if desired.
The image below shows the site structure on the left and the menu automatically displaying them as items.
Editors may choose which folders they want to display in the top horizontal navigation by checking yes or no in the "display page in navigation" section of the EDIT window.
The asset tree (Site Content menu) displays your folders and pages in alphabetical order but your menu items should always be displayed in order of importance. To adjust the order of your top menu items: