Related products can be shown by following 2 steps:-
1.Creating groups: The groups in which related products are to be grouped with specific name.You can choose one or more products which are related to each other and assigned it to a group.
If a you want to create a new product, all you have to type the group name and press enter.
To create a new group must follow these steps:
You can also assign new products to a group:
2.Publish Related Product Module:
After you have created groups go to Joomla backed->Manage->Module->New
and create a Sellacious Products Module with related selected in it
select this option for 'Related products for'
give position this module in template and publish it. Now related products will show on details page.