The right sidebar

This is a classical position, ideal for category list, cloud tags, etc. Its widgets for a comprehensive navigation may be located in this area with easy access.

The bottom sidebar

Or rather, the bottom bar can be used to put information of secondary navigation. If you do not define any widget in this bar, then it will not show the bottom sidebar.

In addition, the sidebar will be visible only in querys that are not pages, or if you use the template of a single column with bottom sidebar, like this page.