Inside of classes are two kinds of things: methods and fields (or properties). Methods can store the code for doing actions; in this example you could have a drive method and a brake method, and maybe a turnRight and turnLeft method. Fields store data; you could have a color field, a speed field and a size field. You can call methods by first making an object of the Car or Truck class, and call it for example ferrari, and doing ferrari.methodName(). In this case, if we wanted to make the vehicle move, we could do ferrari.drive().