The movie above is silent. It shows how to create a new XML file of the type managed by the application. It shows you can drag items into certain regions of the visual designer, i.e., items in the Header category of the Palette can only be dropped in the top of the three widgets, items in the Body category only in the middle, etc. Then right-click anywhere to serialize into the XML file.
Even though it's got HTML in the name, it's simply a visual designer for XML files. After that, the idea is that the XML files get converted to HTML.