Struggling to install and implement Similar Posts ( V: 2.6.2.0) WPress plugin.

Hi Flynn
Congrats on a great theme series and forum.
Can you help me please regarding the use of the “Similar Posts ( V: 2.6.2.0) wp plugin?

I’m trying to get the similar post published at the bottom of my posts - To make this sit comfortably on the page I’d like to add a title (H1) Related Articles:-

In his article “Wordpress Tutorial - Adding Similar Posts” Andy, of Affiliate-Minder.com, recommends that after downloading the plugins you :- …..
……. you need to edit the single.php template if it exists, and if not, either create that file using the index.php

Edit the template in a text editor, and add the following code to the template at the point in your page where you want the similar posts to appear:
<h1>Related Articles</h1>
<?php similar_posts(); ?>
Here you can see it in my Affiliate Minder site’s index.php template:…….

.. A simple question please what the devil is he talking about? Can you point me in the right direction to do this please?
Thank you in anticipation that you feel you can help
Pano