We can achieve so many things by using the custom fields tab of the product we want to show related products of. But this is simpler than other custom fields recipes, in that we don't have to create a custom field first. Showing related products is often a good idea as it encourages customers to make more purchases.
Make sure you have created the products you want to use as related products.
We have created Joomla! the Movie and we will be making it a related product to the VirtueMart the Movie product. Here is how to do it: