Just surrond the class definition with the namespace definition, like
this:

namespace MyNameSpace
{
  class MyClass
 {
   ...
 }
}

re:
!> I want to create a namespace.  I don't know how to do it.

Just write the namespace's name in the different files,
and place all the files in the App_Code directory.

namespace GeometricShapes
{
   public class Square
   {
       public double Side;
   }
}

class Geometry
{
   void ShowSquare()
   {

// in this class you call the Square class of the GeometricShapes namespace :

        GeometricShapes.Square sqr = GeometricShapes.Square();
        sqr.Side = 24.55;
   }
}

If you want a *class* to span several files, make sure they're declared as *partial* classes :

With Partial declarations for a class you can split the class into several files:

MyClass1.cs:

public partial class MyClass
{
public void method1()
  {
// ...whatever you code here
  }
}

MyClass2.cs:

public partial class MyClass
{
public void method2()
  {
  }
}

Juan T. Llibre, asp.net MVPasp.net faq : http://asp.net.do/faq/foros de asp.net, en español :