How does health insurance work in terms of payment?

Let's say there's a family, and there's three different prescriptions for different medications within the family. Let's say the Dad is paying for health insurance. Do you just pay for health insurance once, when you register for it? Do you pay $20 monthly? Does the price you pay go up when you add more medications? I'm confused.
--------------------
If it truly is health insurance, the price is generally quoted on an interval basis, say six months. Often the payments are divided to a monthly basis for convenience. The price of your health insurance is not typically affected by changes in your health status -- that's the whole point of health insurance. When you obtain medical care, prescriptions, or the like, some portion is typically paid by you and some portion is typically paid by your insurance company. The provider or pharmacy bills both you and your insurance, and you pay your share (called a 'co-payment') directly to the provider.
Source