This is a widgeted area which is called Homepage. It is using the Dynamic Content Gallery plugin and the Genesis - Featured Posts widget to display what you see on the Streamline child theme demo site. To get started, you'll need to download the plugin from the link given in the Streamline child theme's README file. Then log into your WordPress dashboard, and then go to the Appearance > Widgets screen. There you can drag the Dynamic Content Gallery widget and the Genesis - Featured Posts widget into the Homepage widget area on the right hand side.