That's basically all they deal in. You request food from a restaurant at an agreed upon price. You receive and eat the food. You now owe the restaurant money - you are in debt. You can pay the restaurant directly on the spot, or you can have your people pay their people by providing them your credit information.

If you pay before eating, then the restaurant is in debt until they have fulfilled their contract to provide your food.

The case could probably be made that to go orders paid on the spot do not have anyone incurring debt.