Sidebars & Widgets
The Sidebars & Widgets panel in the Customizer will display sections for each sidebar that is available in the view currently shown in the Customizer’s preview pane. So if, for example, the preview pane is showing a page, and you’ve configured pages to display the Left Sidebar (in the Pages section of the Content & Layout panel), you’ll see the Left Sidebar section, along with however many Footer Column widget areas you’ve set up in the Widget Areas section of the Footer panel.
Don’t forget! With Make Plus installed and activated, you can also widgetize any column in a Columns section. Ah, the possibilities are endless!