To add to what Rick has said, think of classes as cars: I have a car, you have a car - but they aren't the same vehicle as mine is a black Mercedes, which your's is a blue BMW.
You can have passed a test to drive a car, but unless you select the right vehicle you can't drive to the shops: you have to select YourCar not MyCar because the key will only fit one vehicle.
Car is a
class
: your car and my car are
instances
of the Car class that are held in different variables: YourCar and MyCar, as well as in ThisCar and ThatCar.
"This car" may also refer to your car, "that car" may also refer to my car, and anything you do to ThisCar will affect your actual vehicle: this is called a
reference
to the actual instance
But first you have to create the appropriate instances which needs the
new
keyword:
Car MyCar = new Car("Mercedes", "A180", Black");
Car YourCar = new Car("BMW", "M5", "Blue");
Car ThisCar = YourCar;
Car ThatCar = MyCar;
Console.WriteLine(ThisCar.Color);
Console.WriteLine(YourCar.Color);
ThisCar.Color = Green;
Console.WriteLine(ThisCar.Color);
Console.WriteLine(YourCar.Color);
Console.WriteLine(ThatCar.Color);
Console.WriteLine(MyCar.Color);
Will show:
Blue
Blue
Green
Green
Black
Black
Because both ThisCar and YourCar refer to the same actual vehicle, which is independent of MyCar.
Make a little more sense now?