Navigate to Admin > Appearance > Menus From Admin Panel’s Sidebar.
Please follow below steps to setup onepage menu.
Step 1: Create new menu using custom links as shown in below image. Define menu name (like onepage-menu), add URL with #tag and add link text ( like Home, About Us, Contact Us….) and click on “Add to Menu” button.
Step 2: Expand menu item just added by you and mark checked to “Enable Onepage For This Item (Only For Main Parent)”
Step 3: Repeat above same steps to create new menu items like About us etc…
Step 4: If you are done with all menu items then click on “Save Menu” button
Step 5: Go to page in which you want to set this new one page menu. Select menu that you have recently created in h-Code Page Settings > Header as shown in below image.
Step 6: Now assign id to sections(RAW) in page content, click on edit raw as shown in below image.
Step 7: click on “Extras” tab in Raw Edit popup as shown in below image, add menu item url without # tag (suppose you have used #home as menu url then you needs to use home as extra id). Repeat same step for all raws of page to assign id to raw.
Step 8: Done, You can check one page menu preview in front-end.