This page layout is set to “Content Right, Sidebar Left.” Below, is 1 column with a Sidebar in it. You can see that there are margins and a box shadow on this page. This page is ideal for having Widgets in a Sidebar all the way to the left. You can get creative and add some sidebars below though.
To add a Sidebar to the left, in the sidebar section, go into Appearance/Sidebars from the WP Dashboard. Simply create or locate the Sidebar you like, and then assign the sidebar to a specific page or multiple pages by checking off a page to the left.
You can adjust the section size to make the content area bigger and you can also adjust some other layout options in the Custom Css section in Cornerstones settings tab (such as background colors and shadows).