How to export my object to excel file and download the file as well ?

For converting the List of objects of your class in a excel file and to make it forcefully download as well, you need to create following methods

   
        public void ExportToExcel(object items)
        {
            System.Web.UI.WebControls.DataGrid grid = new System.Web.UI.WebControls.DataGrid();
            grid.HeaderStyle.Font.Bold = true;
            grid.DataSource = items;
            grid.DataBind();
            StringWriter sw = new StringWriter();
            HtmlTextWriter hw = new HtmlTextWriter(sw);
            grid.RenderControl(hw);
            SendFileToBrowser(sw,"MyFileName");
        }

        public void SendFileToBrowser(StringWriter stringWriter, string fileName)
        {
            string attachment = "attachment;filename=" + fileName + ".xls";
            HttpContext.Current.Response.ClearContent();
            HttpContext.Current.Response.AddHeader("content-disposition", attachment);
            HttpContext.Current.Response.ContentType = "application/ms-excel";
            //following two lines to support languages other than english as well.
            HttpContext.Current.Response.ContentEncoding = System.Text.Encoding.UTF8;
            HttpContext.Current.Response.BinaryWrite(System.Text.Encoding.UTF8.GetPreamble());
            HttpContext.Current.Response.Write(stringWriter.ToString());
            HttpContext.Current.Response.End();
        }

For using the above code you can just simply call the "ExportToExcel" method with providing your list as shown below

       List<MyClass> listOfMyClass = new List<MyClass>();
       //Fill the data from your data source
       //Call the following method
       ExportToExcel(listOfMyClass);