create dll in c#.net program

See more:

C#

Hi,
Can anybody give me an example how I can create a dll for c#.net and how I can use the dll in other programs or projects?
Thanks

I have tried after Abhinav link then use a classlibrary file and method is Add

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace math
{
    public class AddClass
    {
        public static int Add(int x,int y)
        {
        return(x+y);
        }
    }
}

and main block like this

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using math;
namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            int a = 2, b = 3;
            int add = AddClass.Add(a , b);
            Console.WriteLine("total", add);
        }
    }
}

Error is A project with an output type of library can not be started directly??

tell me where is wrong??