Certain templates have an editable region along the side of the main content area, called the sidebar. Not all templates have this functionality built in. The templates that do have a sidebar display a note in the template selection that the sidebar is available, as shown below.
Editing the Sidebar
After applying a template with the sidebar feature, you can then add content to the sidebar. To do this, edit a page that you would like to add sidebar content to. A button called "Edit Sidebar" will appear along the top of the page editor, as shown in the image below.
Clicking the "Edit Sidebar" button displays the sidebar's cell(s). (The number of cells depends on how many sidebars are integrated into the template). Use the objects along the top to drag and drop content into the sidebar cells, shown below. Save the page and the sidebar content should then appear on your site.
Additional Options: Two other options are available on the box: "Copy" and "Default?" The Copy option allows you to copy content from the sidebar on another page. After you check the box, a drop-down will show that lets you select the page to copy from. Checking the Default checkbox makes the sidebar's content display on all pages by default.