Go to Appearance –> Menus
Select a menu to edit: (typically Main Menu, perhaps the footer menu too)
Be sure to press ‘Select’
Under ‘Add menu items’ click Custom Links
URL: enter a slash in the URL field then copy and paste the slug from your newly created page at Dashboard > Pages > All Pages > Quick Edit (you may have to open a second window).
Your URL should loo like this: /sample-page-slug
Link Text: the name of the page link as it will appear in the navigation menu (ie: Modern)
Press ‘Add To Menu’
Your new page will now appear at the bottom of the ‘Menu structure’ on the right.
Hover your cursor over the new page until 4 arrows appear
Click, hold and drag your new page up to where you would like it to be on the navigation tree.
Note that you can move it slightly right to make it a sub (child) page of a prior (parent) page.
Press ‘Save Menu’ and then double check your work.