As WordPress changes in 2019, I will keep this page updated of those changes so you can get the most out of the book.
October 23, 2018 – YARPP has been discontinued
Thanks Alan Heckman for the heads up on this.
Typical that only days after publishing the book, a plugin has disappeared. The YARPP plugin is one that I have used for many years, so it is sad to see it go. Fortunately there are a wealth of alternatives. I have been testing a large number of related post plugins this morning. I wanted to recommend one that was simple to use, automatically adds related posts, but offers the flexibility for those that use Page Builder plugins. It was a difficult task. I recommend that you actually try out a few yourself to see which one best suites your site and setup. The one I usually fall back on if YARPP didn't behave is called Contextual Related Posts, but that one was not working on my test site using Elementor Page Builder. If you want a fully fledged related posts plugin, I do recommend you try that one.
There was one plugin that met all of my criteria, though I have never used it before. It was this one:
You can find it by searching the repository for Related Posts for WordPress.
Once installed and activated, it's easy enough to set up.
After activating the plugin, it will go through a process of caching your posts. You'll then have this screen:
Select the number of related posts you want, then click the Link Now button.
In the Settings menu in the left sidebar, you now have a Related Posts item. Go there to configure the output of the plugin. At the top of the settings, I recommend you check the cache option.
You can pretty much leave all of the other options and check your posts. Does the related posts section show up? If so, then go back and look at the settings to see if you want to tweak the output. Towards the bottom of the settings are the Thumbnail Settings. You can specify whether you want thumbnail images next to the related post entries, or just text. If you want just text, then scroll even further down to the Styles section and select Text Only.
That's it. Have fun!