OK this may be a dumb question but how do married folks NOT have babies?

How do they decide not to have babies?

How does the biology work?

I thought a woman was technically able to have babies every ten months (one month of rest after the last baby pops out). In fact how DO married folks not have tons of kids?
Is there some kind of biological mechanism that you get as a married person that enables you to shut down your ability to make babies?
