Health insurance is like a promise or an agreement you have with a special company called an insurance company. You make a deal with them that says if you get sick or need to go to the doctor or the hospital, they will help pay for it.
In the United States, there are many different types of health insurance. Sometimes your parents have health insurance through their jobs or your school might offer you health insurance. Sometimes you have to buy it yourself from a special place called the "Health Insurance Marketplace".
When you have health insurance, you usually have to pay some money every month to keep it, but it's not usually a lot of money. That money is called a premium.
When you go to the doctor or the hospital, they will send a bill to your insurance company. Sometimes you have to pay a little bit of the bill yourself (called a copay), but most of the bill will be paid by your insurance company.
Overall, health insurance is important because it helps take care of you when you get sick or hurt without you having to worry too much about how much it will cost.