Hello, Deb, and welcome to BYC! Glad you joined.
They keep themselves warm in the winter if you keep their coop well ventilated and DRY, 1/2" hardware cloth covering all openings and hot wires will keep them safe.
Check out the Learning Center link you've been given, there are a lot of helpful articles there to help you get off on the right foot. And I agree...a well ventilated, dry coop will keep your flock warm enough through the winter.