In products.tpl OR products_t.tpl you use this code...
Code:
{rating_bar id=$products[product].productid}
It's clearly stated in install.txt
Also, if you want to modify any of your ratings, you can use this SQL patch...
eg. to change product with product ID 123 to a rating of 4 stars...
Code:
UPDATE ratings SET total_votes = 15, total_value = 60 WHERE id = 123;