When you purchase health insurance, the money you pay (your "premium") is combined with the premiums of others to form a pool of money. That money is then used to pay the medical bills of participants who need health care. Your coverage remains valid only as long as you continue to pay your premiums. Once you purchase insurance, the insurance company will give you an insurance identification card for you to use when you seek care from a hospital or doctor.
The insurance company will also provide written instructions for reporting and documenting medical expenses ("filing a claim"). The insurance company will evaluate any claim you file and make the appropriate payment under your policy. In some cases the insurance company pays the hospital or doctor directly; in others the company will reimburse you after you have paid the bills.