C# のオブジェクトとクラスの違いは何ですか?

Box Box1 = new Box();

Box1.height = 3.0;

Box1.getVolume();

using System;

namespace BoxApplication {
   class Box {
      private double length; // Length of a box
      private double breadth; // Breadth of a box
      private double height; // Height of a box

      public void setLength( double len ) {
         length = len;
      }

      public void setBreadth( double bre ) {
         breadth = bre;
      }

      public void setHeight( double hei ) {
         height = hei;
      }

      public double getVolume() {
         return length * breadth * height;
      }
   }

   class Boxtester {
      static void Main(string[] args) {
         // Creating two objects
         Box Box1 = new Box(); // Declare Box1 of type Box
         Box Box2 = new Box();
         double volume;

         // using objects to call the member functions
         Box1.setLength(6.0);
         Box1.setBreadth(7.0);
         Box1.setHeight(5.0);

         // box 2 specification
         Box2.setLength(12.0);
         Box2.setBreadth(13.0);
         Box2.setHeight(10.0);

         // volume of box 1
         volume = Box1.getVolume();
         Console.WriteLine("Volume of Box1 : {0}" ,volume);

         // volume of box 2
         volume = Box2.getVolume();
         Console.WriteLine("Volume of Box2 : {0}", volume);

         Console.ReadKey();
      }
   }
}

Volume of Box1 : 210
Volume of Box2 : 1560