How can we create custom controls in asp.net

In the Visual Studio There is option of creating Web Custom Control.

Here i m giving one very basic example which is msdn.

using System;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace CustomControls
{
      public class FirstControl : Control
      {
            private String message = "Hello";
           
            public virtual String Message
            {
                  get
                  {
                        return message;
                  }
                  set
                  {
                        message = value;
                  }
            }
           
            protected override void Render( HtmlTextWriter writer)
            {
            writer.Write(" "
                        + this.Message + "
" + "The time on the server is " + System.DateTime.Now.ToLongTimeString()
                        + "");
                 
            }
     
      }
}