how to create own exception in c sharp

how to create a exceptionn

friends today i will tell how to create own exception .

using System;

namespace rahul

{

class ownexception

{

  static void Main(string[]args)

{
           firstexception fs=new firstexception();
          try
           {
                fs.dowork();
            }
          catch(Myexception e)
           {

                    Console.WriteLine("exception handle {0}",e.message);



            }
Console.ReadLine();

}

}

}

public class Myexception:applicationException

{

        public Myexception(string message):base (message)

        {

         }

}

public class firstexception

{

int sum=0;

int count=0;

float average;

public void dowork()

{
        if(count==0)

        {

               throw(new Myexception("zero count in dowork"));

         }

else 

averge=sum/count;

}

}