To create a one page website, you need to create a new page first under Pages > Add New:

Next, click on the Use Divi Builder button and add a few modules that you would like to use or load one of our premade layouts.

To set this page as the front page of your website go to Settings > Readings and set the page as Homepage:

In case if you do not need the primary navigation and footer, you can use the blank page template.

However, if you have a lot of content on the page, you may want to add navigation or side navigation to make it easier to navigate through the page.

First, add the CSS ID to any section or module on the page in Advanced settings:

Note: CSS ID should not contain any spaces or special characters. 

CSS ID should be unique for each section or module, you can't use the same CSS ID twice on one page.

Copy the CSS ID and add it as custom link to the menu in Appearance > Menus:

Make sure to add # before the CSS ID when you add link to the menu.

That's it! Once you click on that link in the menu, it will scroll down to the section or module with the CSS ID.

The side navigation which you can see at the right side on this example can be enabled in Divi Page Settings: 

The amount of dots depends on amount of sections that you added to the page.