This is the basic method to use DataReader

con = new SqlConnection(ConfigurationManager.ConnectionStrings["YourString"].ConnectionString);
            con.Open();
            string str = "SELECT Field1.Field2. field3 FROM table";
            SqlCommand cmd = new SqlCommand(str, con);
            SllDataReader dr = cmd.ExecuteReader();
            dr.Read();
            YouRGridView.DataSource = dr;
            YourGridView,DataBind();
            con.Close();

To get  a field from reader,

 If it is a string value in fiirst column it can be obtained as

 dr.GetString(0)