How to Call Web Service ?

using System;
using System.Collections;
using System.Linq;
using System.Web;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Xml.Linq;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Collections.Generic;
using AjaxControlToolkit;
using System.ServiceModel.Web;
using System.Xml;

[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line.
[System.Web.Script.Services.ScriptService()]

public class CreatePOWS : System.Web.Services.WebService
{
   public CreatePOWS()
    {
        //Uncomment the following line if using designed components
        //InitializeComponent();
    }

//If you want enable session and call this method in server side then uncomment the below line
//[System.Web.Services.WebMethod(EnableSession = true)]

//WebMethod used to call this method in client side
    [WebMethod]
    public string HelloWorld()
    {
        return "Hello World";
    }
}


//After that create object for call webservice in serverside

CreatePOWS  obj_CreatePOWS =new CreatePOWS ();

Response.Write(obj_CreatePOWS.HelloWorld());

//For ClientSide Call add the following lines inside the form

<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePageMethods="true">
         <Services>
          <asp:ServiceReference Path="~/Service/CreatePOWS.asmx" />
         </Services>
    </asp:ScriptManager>


//then script call webservice methods through
alert(CreatePOWS.HelloWorld());