Design Setting

Archive Settings

Go to Appearance >> Customizing >> Design Settings >> Archive Settings.
Choose the archive sidebar from available options.
Choose the archive content layout from available options.

Page Settings

Go to Appearance >> Customizing >> Design Settings >> Page Settings
Choose sidebar from available options for a single page.

Post Settings

Go to Appearance >> Customizing >> Design Settings >> Post Settings
Choose sidebar from available options for a single post.

Click on Related Post OptionĀ  to show Related Posts.