using System;

public class Dog
{
        // Notice how both methods have the same name
        public void MakeNoise()
        {
                // No parameters?  Bark!
                Console.WriteLine("Bark!");
        }

        public void MakeNoise(string noise)
        {
                // Otherwise make the noise specified
                Console.WriteLine("{0}!", noise);
        }

        static void Main()
        {
                // Create a new instance of the Dog class
        Dog lassieTheRetriever = new Dog();

                // Sometimes Lassie may bark, sometimes she may
                // yip, it depends on the situation.
                lassieTheRetriever.MakeNoise();
                lassieTheRetriever.MakeNoise("Yip");
        }
}

Bark!
Yip!

using System;

public class Dog
{
        // Every healthy dog can walk, right?
        public void Walk(int distance)
        {
                Console.WriteLine("Walked {0}m", distance);
        }

        public static void Main()
        {
                // Create a new instance of GoldenRetriever named
                // lassie, then walk 10m
                GoldenRetriever lassie = new GoldenRetriever();

                lassie.Walk(10);
        }
}

// Empty class we will take advantage later
public class GoldenRetriever : Dog
{

}

Walked 10m

using System;

public class Dog
{
        // Many dogs have their own tricks
        public virtual void PerformTrick()
        {
                // This method will be overwritten later :-)
        }

        public static void Main()
        {
                // Create a new instance of GoldenRetriever named lassie
                GoldenRetriever lassie = new GoldenRetriever();

                // Lassie needs to do a trick now
                lassie.PerformTrick();
        }
}

public class GoldenRetriever : Dog
{
        public override void PerformTrick()
        {
                Console.WriteLine("Fetch!");
        }
}

Fetch!

using System;

public class Dog
{
        // Every dog has some properties, they just vary
        // from dog to dog.

        // We don't want anybody but the setters and getters
        // touching our properties.  Otherwise they may touch them
        // in inappropriate ways.  By using this method we restrict
        // ways the values can be modified.
        private int    _numberOfLegs = 4;
        private string _furColour    = "Blonde";


        // Notice how these "methods" contain no parameters nor
        // parenthesis and their names match those of the property
        // variables, only they are in Pascal Case instead.
        public int NumberOfLegs
        {
                get {
                        // Also notice the prefix on property variables
                        return _numberOfLegs;
                } set {
                        // value is a special object that holds
                        // the new value passed to this block.
                        _numberOfLegs = value;
                }
        }

        public string FurColour
        {
                get { return _furColour; }
                set { _furColour = value; }
        }

        public static void Main()
        {
                // Create a new instance of GoldenRetriever named lassie
                GoldenRetriever lassie = new GoldenRetriever();

                Console.WriteLine("Lassie\'s coat is {0} in colour and she has {1} legs", lassie.FurColour, lassie.NumberOfLegs);

                // Create another GoldenRetriever object named rebelBailey
                GoldenRetriever rebelBailey = new GoldenRetriever();

                // Sadly he only has 3 legs, and a purple coat
                rebelBailey.NumberOfLegs = 3;
                rebelBailey.FurColour    = "Purple";

                // Now display Rebel Bailey's modified properties
                Console.WriteLine("Rebel Bailey\'s coat is {0} in colour and he has {1} legs.", rebelBailey.FurColour, rebelBailey.NumberOfLegs);
        }
}

// A breed or "subclass" of Dog
public class GoldenRetriever : Dog
{

}

Lassie's coat is Blonde in colour and she has 4 legs
Rebel Bailey's coat is Purple in colour and he has 3 legs.