If you get sick, you just go to the doctor.

At no point you worry whether you can afford it.

The doctor looks at you and makes a list of what they think you need. At no point they ask you what you can afford. You just get what you need. It might be going through a multi-million dollar machine, operated by a very well paid specialist. No matter. You get sick, you get the machine. The CEO of some bank gets the same sickness, they gets the exact same prescription.

Depending on the details of the implementation, when it's all over, you're free to go, there's nothing to pay. In some implementations, there's a bill. But, you usually have enough change on you to pay it. It's very cheap, and doesn't actually cover the costs at all. Some implementation require people to pay a symbolic amount to avoid stuff like lonely people pretending to be sick just to have someone to talk to.

So, who pays? Taxes. It's not cheap either. Billions upon billions. But that's a choice societies make, and pretty much all societies that have the cash make the Universal Healthcare choice. I know of only one exception.

Muricka.