Health Care is very expensive in the USA and quite different from other countries. In many countries the government pays for health care for its citizens while in the United States individuals are responsible for these costs themselves. The USA has a pay-for-services system. Without insurance, an office visit to see a doctor for a minor illness costs between $200 - $400; a "normal" pregnancy and delivery care will cost at least $12,000; an appendectomy with two nights in the hospital could easily be $20,000.
These potential fees are the reason why you must purchase health insurance!