Here is a stab at an explanation. With whirlpool, your coin is broken into multiple smaller coins. Each smaller coin is then swapped with a random coin from a bag of other same sized coins. You control up to how many times you want to do a swap with your smaller coins. The privacy comes from the fact that you are randomly swapping coin histories when you swap coins. The more swaps that are performed the lower the chance that any one coin history is your history. The cost is an initial transaction fee to enter he whirlpool but you don’t have to pay for additional mixes while you remain in the whirlpool.