Citizens buy medical insurance to see a doctor, and they buy commercial insurance instead of social security. If there is no insurance in America, no one can afford it except the rich, so you must buy insurance. Insurance is divided into PPO and HMO. If you have money and love to travel, the advantage of buying the former is that you can see a doctor in all hospitals in the United States. If not, you can buy the latter, but the patient must go to the hospital designated by the insurance company to be reimbursed. Many hospitals don't reimburse cheap insurance. The reimbursement ratio depends on the insurance you buy, and the expensive ones are over-reported.
Medical insurance is divided into medical insurance, drug insurance, vision insurance and dental insurance, and general companies only provide the first two.
You can buy insurance with your family in America. Generally, it is a big head of the company and a small head of the individual. But it's also expensive. A good insurance individual must pay 1000 USD every month.