Getting a Billing Contract

Hello All,
It is me again with another maybe rookie question where most of you will think I have no idea what I am doing, but how do you get a billing contract. Do you call the insurance company's Finance department or how does it work?
It is me again with another maybe rookie question where most of you will think I have no idea what I am doing, but how do you get a billing contract. Do you call the insurance company's Finance department or how does it work?