The plugin shows related category posts in your post content.
Related Category Posts is a free WordPress plugin that allows to embed in any post are related to your post category links. What you need is to install and activate the plugin through the 'Plugins' menu in WordPress.
1. Upload the entire related-category-posts-plugin folder to the /wp-content/plugins/ directory
2. Activate the plugin through the 'Plugins' menu in WordPres