打6折 means the item is 40% off of its original price. If this is confusing, it may help if you think of it as COSTING 60% of the normal price. It's a strange system, I know.

6折 means you get item by paying 60% of the original price. that is 40% off from the original price.

на пальцах 6打折 значит что Вы платите 6 частей от первоначальной цены

6折=40%discount

Yeah, as it is interpreted above, after discount/打折, now it only costs (n*10)% of the normal/original price. And it means that item of goods is taken (10-n)*10% off the original price. *n->打n折* Here 折 ≠ off.