A URL is not used to specify navigation or structure of the site. This means that a URL site element only can be used as a child in the site structure, never as a parent.
The explanation given on this page is mostly meant to give an understanding of the role of URLs in the site structure. A detailed description of how to insert a URL in the site structure can be found here.
This section will describe what it means that a URL is a child of a site element of a specific type.
In this case the URL site element have two different roles.
1. As it is a child of a menu site element, it will be used to show a menu item in the menu defined by the menu site element.
2. When the menu item is pressed, the URL will be used to populate a sub-frame (identified by the frame name specified when the business process was attached to the menu). The frame specified will be populated with the HTML page returned when accessing the URL address specified in the URL site element.
In this case the URL will be used to populate a sub-frame specified by the frameset as the frameset is loaded.