Inside the WordPress admin area, go to Pages and edit the page on which you want to set up the one page layout (usually Home). Click on "Row Settings" and add a "Row ID" for each row, where you want to have your navigation scroll to. For example, if you want the "About Us" section to be linked in the menu, you would edit its row and add an "about-us" ID to it.

Then go to Appearance - Menus and on the left side open the "Custom Links" tab. For the URL field write the full url path to the "One Page" layout page and add the ID (starting with "#") at the end of it. Example: For the link text write the label of the link (what the user will see). Example: "About Us". Repeat this part for all the IDs you have set.