How to validate a textbox control Asp.Net

I am learner of asp.net and trying to using customvalidator but when I use the following codes showing some errors
please help any one to get the solution.

.aspx file 


<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>







   


   

   

   
        Enter Your Name:
       
   
       

       

                              
       
       

   
       

   
   

   

aspx.cs file


using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;


public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {


    }
    protected void CustomValidator1_ServerValidate(object source, ServerValidateEventArgs e)
    {
        if (e.Value.Length == 8)
        {
            e.IsValid = true;
        }
        else
        {
            e.IsValid = false;
        }
    }
}


Error Log:

WebForms UnobtrusiveValidationMode requires a ScriptResourceMapping for 'jquery'. Please add a ScriptResourceMapping named jquery(case-sensitive).

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.InvalidOperationException: WebForms UnobtrusiveValidationMode requires a ScriptResourceMapping for 'jquery'. Please add a ScriptResourceMapping named jquery(case-sensitive).

Source Error: 

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

please support how to use jquery.