Adding links to page sections

Each section has an “add to menu” button that will add a menu element that links directly to that section. This can be very useful if you want to quickly create a menu for a one page site. To change the label of the menu button, just click the section title and change the text - it will update in the menu, too.

For more advanced menu editing (like reordering the buttons, creating submenus, etc) please use the “Menus” section of the Customizer. See more here https://codex.wordpress.org/Appearance_Menus_Screen