How to Read Value from Web.Config

string[] Value = System.Configuration.ConfigurationSettings.AppSettings.GetValues("TransactionSlip");
                    if (Value[0].ToString() == "1")
                    {
                        tblHeader.Visible = true;
                        DataSet dsHeader = ObjBillingBL.GetCentreHeaderContent(Convert.ToInt32(Session["CenterId"]));
                        LblHeader1.Text = dsHeader.Tables[0].Rows[0]["ADDRESS1"].ToString();
                        LblHeader3.Text = dsHeader.Tables[0].Rows[0]["ADDRESS2"].ToString();
                        LblHeader4.Text = dsHeader.Tables[0].Rows[0]["ADDRESS3"].ToString();
                        LblHeader5.Text = dsHeader.Tables[0].Rows[0]["PhoneNo"].ToString();
                    }
                    else
                    {
                        tblHeader.Visible = false;
                    }