How to use subclass of Control

Dear all,
         I have a subclass Calendar in a cs file. The file is as follows, and I put it in directory named "Test/DataCalendar.cs" .
using System;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
namespace DataControls
{   
    /********************************************************
      Class DataCalendarItem
        - serves as the container for a single calendar entry,
          allowing for databinding syntax like the following
          to be used in the .aspx page:
         
            <%# Container.DataItem("MyField" ...