I don't use Uber eats, or any other service. How does it work? Does the restaurant pay the full cost? I would have assumed it was free to the restaurant and the

I don't use Uber eats, or any other service. How does it work? Does the restaurant pay the full cost? I would have assumed it was free to the restaurant and the customer pays the delivery free. If that was the case, then why is there a cap? But I'm assuming that isn't the case... Then how did deliver services ever get to charging the restaurant?