The below code snippet explains how to implement jQuery UI DatePicker
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.6/jquery.min.js" type = "text/javascript"></script>
<script src="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/jquery-ui.min.js" type = "text/javascript"></script>
<link href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/themes/base/jquery-ui.css" rel = "Stylesheet" type="text/css" /> 
<script type = "text/javascript">
    $(document).ready(function () {
        $("#txtDate").datepicker();
    });
</script>
<input type = "text" id = "txtDate" />
 
Explanation:
In the above code snippet in the document ready event handler of jQuery simple datepicker has been applied to HTML input textbox txtDate
Demo: