Using jQuery

Use the jQuery built-in to WordPress and ALWAYS use the wp_enqueue_script() function to add your scripts correctly.

http://codex.wordpress.org/Function_Reference/wp_enqueue_script

So, to use jQuery on the front end of your site use something like:

function add_jquery() {
    wp_enqueue_script( 'jquery' );
}
add_action('wp_enqueue_scripts', 'add_jquery');