The name "Sidebars" is used very loosely here. These fields are essentially 4 "metafields"--i.e., fields used for special, custom purposes. They are typically used with custom formats and collections.

Important note: unless we have set up a custom format or collection for you, these Sidebar fields will not be active on your website--i.e., any content you put in them is not going to show up in your articles.

In custom formats, these are usually used for elements such as sidebars or lists, etc. An example would be the videos and right column checklist here in this Welcome Aboard page.

In custom collections, these fields are usually used for sorting and categorizing purposes. An example would be how this list of clubs is categorized by region here.