Place a HTML container on the stage (1).

Select the Web Container on the stage and add the desired HTML archive via the widget properties inspector (circle icon) (2) with the "+" button (3).
Note: The HTML file must be a zip file. It should contain all the data required for proper HTML function, including the appropriate JavaScript and CSS files and all integrated media data (images, etc.)

In the list, select the HTML page that should be displayed as the start page in the Web Container (4). 
Note: With the "Preload Content" option (5), the web container's content is pre-loaded as part of the page pre-loading. This is useful if the Webview makes up a large part of the page. Otherwise, the contents of the Webview will be loaded as soon as it enters the area visible to the user.