Does this health plan mean that folks who don't want insurance still have to buy it?

(Yes, there are still folks out there who don’t want a health care plan.) I’m talking about the people who for whatever reason, don’t want to sign up. Also, what about the people who are here on a visa, or illegal aliens? Do they have to have it, is it optional, or is it denied? What happens to them if they get sick, and land in the hospital anyway, and don’t have the money to pay the bill?