What's the difference between Tortoises & Turtles?

Do Turtles really live inside their shells? What are Turtle shells made of? Why do Turtles walk slow but swim fast? For free home activities sign-up at www.WhoSmarted.com See Privacy Policy at https://art19.com/privacy and California Privacy Notice at https://art19.com/privacy#do-not-sell-my-info .