In the master page's head section, add the links to the libraries
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.5.1/jquery.min.js"></script>
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.11/jquery-ui.min.js"></script>
<link href="../assets/jquery-ui-1.8.11.custom.css" rel="stylesheet" type="text/css">
<link href="../assets/datepickersize.css" rel="stylesheet" type="text/css">
Once you get the libraries, in the content page, drag & drop a asp:TextBox and add the jquery code to attach the datepicker to the textbox.
It should look like below.
<script type="text/javascript">
$(document).ready(function() {
$('[id$=TextBox1]').datepicker({ showAnim: 'slideDown' });
});
</script>
<asp:textbox id="TextBox1" runat="server"></asp:textbox>
If you are not using master page, you can replace $('[id$=TextBox1]') with $("#TextBox1"). Thats it! Just 4 files to link and 2 lines of code will get you a beautiful Datepicker on your page.