To add content to the sidebar (left sidebar or right sidebar) in Drupal, you typically need to work with blocks and assign them to a sidebar region. Here is a step-by-step guide to help you add content to the Left Sidebar and Right Sidebar.
Create a Block
You can create a new block or use existing blocks.
Navigate to: Administration > Content > Block
example.com/admin/content/block
Assign Block to Sidebar Region
Navigate to: Home > Administration > Structure > Block layout
Place the block in Sidebar Left or Sidebar Right region.
Visibility Settings
Under Visibility section of the block, you can configure on which pages this block will appear and which user roles can see this block.