When someone visits your site and reads an article, having a related posts section at the bottom encourages them to keep reading. This also reduces your bounce rate. i.e. The percentage of people who leave your site after visiting only one page.
How to add related posts to WordPress
1. Install the Yet Another Related Posts plugin.
There are many other options but this plugin is both easy to use and allows for text or thumbnail listing of related articles at the bottom of every post on your site.
2. Configure the plugin.
After the plugin has been installed and activated navigate to Settings >> YARPP.
In the Display Options section you can customize the heading and whether to show just text links or thumbnails for your related posts. NOTE: for this to work you need to have a featured image selected for each post.
The thumbnails option looks great but I use the text links option as it keeps the pages loading faster.
You can also exclude certain categories in “The Pool” section or refine the “Relatedness” algorithm but I have found it to work well as is.
A lot of websites just have way too much stuff crammed at the end of their articles but adding a related posts section to WordPress is one that increases useability and effectiveness.