integrating jquery with default theme

am trying to integrate jquery with the default blog theme
i tried using wp_enqueue_script('jquery') in header.php but it does not load the jquery.js
jquery file is stored under wp-includes/js/jquery/jquery.js

i tried using this function too
wp_enqueue_script(‘jquery’,'wp-includes/js/jquery/jquery.js');
even this does not work the js file is not loaded at all in both the cases

is there something that I am doing wrong ??