This is a widgeted area which is called Homepage. It is using the Genesis - Featured Posts widget to display what you see on the Platinum child theme demo site. To get started, log into your WordPress dashboard, and then go to the Appearance > Widgets screen. There you can drag the Genesis - Featured Posts widget into the Homepage widget area on the right hand side. To get the image to display, simply upload an image through the media uploader on the edit page screen and publish your page. The Featured Posts widget will know to display the post image as long as you select that option in the widget interface.