White space on either side of the content maintains a proportioned readable line length in your main content. In the current iteration of the DLC theme, this space is maintained by “persistent sidebars“ which is selected by default in the theme appearances menu.
However, you may wish to use the left and right sidebars for adjunct content such as callouts, twitter feeds, or related content. You may wish to add content in these areas on one or two pages only. A more extensive site may require that you have these areas available for such content on all pages.
1) Adding sidebar content on a few pages requires you to create a block and place that block on the page or pages in which you wish the content in that block should appear. Choose this method if you have common sidebar content that you wish to appear on many pages, or if you only have a few pages that require content in the sidebars.
To learn how to add individual sidebar content blocks to pages, go to Adding sidebar content.
2) If your site will require that you have these sidebar areas available on every page, you will want to create structural left and right sidebars that are integral to the page structure and allow you to add content on each page's sidebar areas independently without creating separate blocks. This requires in-depth Drupal work using Views and Blocks, but will increase the usability and long-term content strategy of your site.
To learn how to add content-enabled sidebar columns site-wide, go to Left and right columns.