How to create web services in ASP.NET?

using System.Data;
using System.Data.SqlClient;
using System.Configuration;

/// 

/// Summary description for ClsFun
/// 

public class ClsFun
{
    SqlConnection sqlcon = new SqlConnection(ConfigurationManager.ConnectionStrings["Con"].ConnectionString);
    SqlCommand sqlcmd = new SqlCommand();
    SqlDataAdapter da = new SqlDataAdapter();
    DataTable dt = new DataTable();

    public ClsFun()
    {
        //
        // TODO: Add constructor logic here
        //
    }

    public DataTable getdata(string qry)
    {
        sqlcon.Open();
        sqlcmd = new SqlCommand(qry, sqlcon);
        da = new SqlDataAdapter(sqlcmd);
        da.Fill(dt);
        sqlcon.Close();
        return dt;
    }

    public class empdet
    {
        public string eno = "";
        public string empname = "";
        public string sal = "";
        public bool validuser = false;
    }

    public empdet ChkvalidUser(string id)
    {
        string query;
        empdet s = new empdet();
        query = "select * from emp where eno='" + id + "'";
        dt = getdata(query);
        if (dt.Rows.Count > 0)
        {
            s.eno = dt.Rows[0][0].ToString();
            s.empname = dt.Rows[0][1].ToString();
            s.sal = dt.Rows[0][2].ToString();
            s.validuser = true;
        }
        else
        {
            s.validuser = true;
        }
        return s;
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Services;
using System.Web.Script.Services;
using System.Web.Services;
using System.Web.Services.Protocols;

/// 

/// Summary description for WebService
/// 

[WebService(Namespace = "http://localhost:2323/04WsExample/WebService.asmx")]
[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 EmployeeDetails : System.Web.Services.WebService 
{

    public EmployeeDetails() 
    {

        //Uncomment the following line if using designed components 
        //InitializeComponent(); 
    }

    [System.CodeDom.Compiler.GeneratedCodeAttribute("wsdl", "2.0.50727.3038")]
    [System.SerializableAttribute()]
    //[System.Diagnostics.DebuggerStepThroughAttribute()]
    [System.ComponentModel.DesignerCategoryAttribute("code")]
    [System.Xml.Serialization.SoapTypeAttribute(Namespace = "http://localhost:2323/04WsExample/WebService.asmx")]
    
    //Create class to return more than one values
    public class empResponse
    {
        public string eno;
        public string empname;
        public string sal;        
    }

    [System.CodeDom.Compiler.GeneratedCode("wsdl", "2.0.50727.3038")]
    [System.SerializableAttribute()]
    //[System.Diagnostics.DebuggerStepThroughAttribute()]
    [System.ComponentModel.DesignerCategoryAttribute("code")]
    [System.Xml.Serialization.SoapTypeAttribute(Namespace = "http://localhost:2323/04WsExample/WebService.asmx")]
    
    public class emp
    {
        private string id;
        private string val;

        public string id1
        {
            get
            {
                return this.id;
            }

            set
            {
                this.id = value;
            }
        }

        public string val1
        {
            get
            {
                return this.val;
            }
            set
            {
                this.val = value;
            }
        }
    }

    [WebMethod(BufferResponse = true, Description = "Get Employee Details")]
    [ScriptMethod(ResponseFormat = ResponseFormat.Xml, XmlSerializeString = true)]
    
    //Get employee details using employee numeber
    public empResponse GetEmployeeDetails(string eno)
    {

        empResponse resp = new empResponse();
        
        //Create instance for sqlheleper class
        ClsFun obj = new ClsFun();         
        
        //Create instance for employee details return values 
        ClsFun.empdet obj1 = new ClsFun.empdet();
        
        //Check valid user or not match with database value
        obj1 = obj.ChkvalidUser(eno);
        if (obj1.validuser == true)
        {
            resp.eno = obj1.eno;
            resp.empname = obj1.empname;
            resp.sal = obj1.sal;
        }

        //return over all response value instance
        return resp;       
    }    
}

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        Enter eno<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox><br />
        <asp:Button ID="Button1" runat="server" Text="Submit" OnClick="Button1_Click" Style="height: 26px" />
        <br />
        <br />
        <br />
        <asp:Label ID="lblResult" runat="server"></asp:Label>
    </div>
    </form>
</body>
</html>

using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using localhost;

public partial class _Default : System.Web.UI.Page 
{
    localhost.EmployeeDetails obj = new localhost.EmployeeDetails();

    protected void Page_Load(object sender, EventArgs e)
    {
        //Make sure you add web reference before
        lblResult.Text = "";
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        //Declare isntance for web service class
        empResponse obj1 = new empResponse();
        
        //Get employee all details using eno textbox
        obj1 = obj.GetEmployeeDetails(TextBox1.Text);

        //Write it all details in web page
        lblResult.Text = "Employee No:" + obj1.eno ;
        lblResult.Text = lblResult.Text + "

Employee Name:" + obj1.empname;
        lblResult.Text = lblResult.Text + "

Employee Salary:" + obj1.sal;
    }
}