How to add code to sidebar ?

The plugin uses the ad code that you insert in the plugin settings (WP Admin > Settings > Adsense In-Post).
Once you paste your ad code in one of the blocks, use the appropriate shortcode ([AdSense-A], [AdSense-B], or [AdSense-C]) to insert the ad code inside a page or post.
If you want to use the shortcode in the sidebar, your theme may not allow shortcodes in a text widget. If that is the case, create a child theme, and add add_filter('widget_text', 'do_shortcode'); to your child theme’s functions.php file.