To setup a onepager, two installations from the Upgrade Store are required:
The first step is to implement anchors on the webpage. Double click on the anchor element or drag and drop it to the desired place. Next you give a description to the anchor (i.e. anchor).
Every anchor can be connected with a menu item. As soon as a user clicks on the menu item, he gets redirected to the place on the page where you installed the anchor element. This can be done in the Page Management.
Navigate to page management and choose the page you wanna link with an anchor. On the bottom end of the settings page, you'll have a field URL. There you fill out the description of the anchor, preceded by an # (#anchor). Or add an anchor to any link by choosing external link.
After you clicked the Save button, the menu item is connected with the anchor
The speed of which the redirect is being executed, the amount of pixels above or below the anchor, ... These are all things that can be edited in the SiteManager Design application.