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).
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.