Health insurance is like any other insurance. You bet the company that you will need more medical care than the cost of the premiums. The ocmpany bets you that you won't. And really, you hope that they win!
You pay a regular amount, so that you always have a fair idea about how much or your budget is going for health care. Depending on the level of your health cover, you can choose which doctor and which hospital you go to.
You get to have whatever procedure your specialist recommends, without having to go on a long waiting list.