How do I write a "using" statement connecting the class to aspx.cs file

A using statement works on classes that implements the interface IDisposable.
And the dispose method should release all allocated resources, e.g. close open files, delete memory etc.

Implementing your example in two different ways. The end result is the same.
Not using using:

SqlDataReader dr = null;
try
{
    dr = cmd.ExecuteReader())
    {
        dr.Read();
        n += 1;
        idc.Add(dr[0]);
        dt.Add(dr[1]);
        c1.Add(dr[2]);
        c2.Add(dr[3]);
        c3.Add(dr[4]);  
    }
}
finally
{
    // Always close, even if an exception occurs
    if (dr != null)
        dr.Close();
}

using used:

using (SqlDataReader dr = cmd.ExecuteReader())
{
    dr.Read();
    n += 1;
    idc.Add(dr[0]);
    dt.Add(dr[1]);
    c1.Add(dr[2]);
    c2.Add(dr[3]);
    c3.Add(dr[4]);  
} // The dispose method is called upon leaving the scope

So you need to implement the IDisposable interface in your class

public class MDFtoMDF : IDisposable
{
    public int cid { get; set; }
    public string cdt { get; set; }
    public string cc1 { get; set; }
    public string cc2 { get; set; }
    public string cc3 { get; set; }

    public void Dispose()
    {
        Dipsose(true);
    }

    private void Dispose(bool disposable)
    {
        if (disposable)
        {
            // Free resources
        }
        // Prevents the destructor to be called if dispose is called.
        GC.SuppressFinalize(this);
    }
}

Now you can write the code as below

using (MDFtoMDF test = new MDFtoMDF())
{
    // Do your stuff
}

The thing is that if you don't have resources that must be explicitly released, then the using statement does not add any useful functionality.