no, there is no t a tutorial but all the details are in the linked post. read the rest off the thread i linked to initially.
in the add to cart button behavior, you need to set the value of the discountable column to 1 for items that the discount applies to and 0 for items the discount does not apply to.
you then need to create the discount. set the trigger to number of unique items in the cart > 0. set the calculation to "Based on items with a specific value":
Total of 'TotalPrice' where 'discountable' has a value of '1' 'times' '.15'
