NOTE: You can make the configuration of auto-related products if you use Blog Plus or Blog Extra extension only.
In order to enable related products please go to Admin Panel > Stores > Configuration > Magefan Extensions > Blog, find Post View section and choose Related Products subsection.
1. In the Display Related Products select box enable related products by choosing Yes.
2. In the Enable Auto Related Related Products (Blog+) select box choose Yes to enable auto-related products. The system generates blog-related products automatically by the most frequently used words from your posts and products, thus it is mostly concentrated on the content and title.
3. In the Black Words For Auto Related field enter words which have not been used for search of related products. You don't need to enter one letter words e.g. (I, 1, 2), extension already skip such words.
Once you have finished don't forget to press the Save Config button and wait some time for the system to generate the related posts by cron (~ few hours).