Widgets are independent sections of content that can be placed into any widgetized area provided by your theme. Although these widgetized areas are commonly called ‘Sidebars’ and are quite often located in the left or right-hand column, they can be also located anywhere within your site and are entirely dependent on the current theme as to their location. Lots of themes use these widgetized sidebars in the footer area.
In WordPress 5.8, the Block Editor was integrated into the Widgets screen, and will become the default way to edit your Widgets going forward. However, if you wish to continue to use the old Widgets screen, you can do so by installing the Classic Widgets plugin. The Classic Widgets plugin will allow you to disable the Block Editor and instead, will provide you with the same Widget editing interface that you've been using prior to WP 5.8. The Classic Widgets plugin can be downloaded from the Plugin Directory on the WordPress.org website, or you can install it directly onto your site using the Plugins > Add New menu option and then typing in ‘Classic Widgets’ (without the quotes) in the Search plugins… field.