A heated garage = a garage that is kept warm in cold weather by a heating system, electronic/infrared, forced air, et al.
It must be a fully-finished garage if you want it to be heated. A heated garage can be used a workshop, a heated storage room, a play place, etc.
If you only want to park your car(s) inside the garage, you'd better not to heat it as high temperature can help salt damage your car faster. A heated garage does more harm than protect your vehicle(s) unless you wash you vehicle(s) thoroughly each day.