Using Button and Grideview Export to Microsoft Excel Format

Export to Microsoft Excel Format

please explain this code

protected void Buttonexp_Click(object sender, EventArgs e)
{
Response.Clear();
Response.AddHeader("content-disposition", "attachment;filename=GridView_to_Excel.xls");
Response.Charset = "";
Response.ContentType = "application/vnd.xls";
StringWriter StringWriter = new System.IO.StringWriter();
HtmlTextWriter HtmlTextWriter = new HtmlTextWriter(StringWriter);
GridView1.RenderControl(HtmlTextWriter);
Response.Write(StringWriter.ToString());
Response.End();
}

public override void VerifyRenderingInServerForm(Control control)
{

}