Sidebars are managed with the Custom Sidebars plugin. This plugin allows us to have different sidebars for different posts and pages.
To make new sidebars or changes to sidebars, go to Appearance -> Widgets. To change the sidebar associated with a page or post, you may need to change the Sidebar Location found on the Sidebars section of the Widgets page and the Layout and Sidebars on an individual post or page. Details on this process can be found below. More information can be found at the official plugin site.
This 3 minute video should get you started, with the caveat that some of the options shown are not available in the free version of the plugin we’re using.

All the settings and options for the sidebars are available under Appearance > Widgets.
On the Widgets page you’ll see that all available widgets are shown on the left side. On the right side is the Sidebars section. The Sidebars section at the top enables you to create a new custom sidebar, or export/import your sidebar configuration. The Custom Sidebars section will display the custom sidebars we have created. The Theme Sidebars section displays the sidebars made available by the WordPress theme we’re using (Responsive).

Important widgets

Posts are organized by a hierarchy of categories and tags.  Lists of posts can be built in the sidebar using widgets from the plugins Posts by Tag and List category posts.