Create a menu
Go to Appearance > Menus and create a new menu. The name of the menu is irrelevant. Add pages to the menu. Under Menu settings, set the menu to ‘Primary Navigation’ or ‘Secondary Navigation’. Save the menu.
The primary navigation is designed for using subpages. The subpages will show in a dropdown menu. You can create submenus by placing a menu item under the parent and indent it to the right.