Click 'Insert' in the main toolbar.
From the left sidebar click 'Menu', choose a menu style and click 'Use this'. The menu will be added to your page.
By default, the menu will display all pages and sub pages you have added via the 'Pages' tab (except those you've chosen to hide from the menu!).
To change this, with the menu selected from the floating Editor box click the 'Setup' tab > Padlock icon. Here you have four choices:
All pages - Main pages and sub pages.
Top level pages only - No sub pages.
Sub pages only - When on a page, the menu will only display the sub pages of that specific page. If the page has no sub pages, the menu will be empty.
Shop categories - Displays all shop categories you've added under the Shop tab.