how to produce dll using visual studio?

Hi there,whatever Sergey Sir told is absolutely right but let me help u out.
go to
File Menu->New->Project->Class Library template and click OK.
it will open a Class1.cs page for you.

public class Class1
{
    public int Add(int a, int b)
    {
        return a + b;
    }
}

now build your project .And add another console Application using Add Project tab.
and now Add refresnces of ClassLibrary1 in your console Application(go to Refrences->Add Refrences->Browse->ClassLibrary1Projoect->bin->debug->ClassLibrary1.dll).
and use below code on Program.cs page:

using System;
using ClassLibrary1;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Class1 c = new Class1();
          Console.WriteLine( c.Add(10, 16));
          Console.ReadKey();
        }
    }
}

now run this ConsoleApplication for getting addition using .DLL concept.
Done.

so jmd
:-)