As explained before, you can decide how much you would like to contribute per order to, in this case, Doordash, to minimize the cost of delivery to your customers. If you leave it at $0, the customer will have to cover the total delivery cost of the order. It is important to note that customers cannot see the cost of deliveries until they reach the final step of the delivery process. You can find an example below. 

In this occasion, this venue has decided to contribute with $4 per delivery. This means that, if DoorDash delivery rate is usually $8.7, now the customer only has to pay a delivery fee of $4.7, instead of $8.7. Increasing the amount of money you contribute per order could be an incentive to get more customers to place orders, as the cost of their deliveries will be reduced.