Using Navigation Menu for Adding Subpages

1. In your header, click on the menu settings:
   
   
2. Whether you’ve decided what page to change, hover over it and click on the three dots:
   
   
3. Then click on Convert to subitem:
   
   
4. Note how it should look like on the published site:
   

The article Menu bar settings will present you with tips on customizing your navigation menu.