Put code into body tags near top, using a plugin

Put that script into a file somewhere in your theme folder. Include it using the following code in your theme’s functions.php file:

<?php
function wpa_65602_enqueue_scripts() {
     wp_enqueue_script( 'facebook', get_bloginfo( 'template_url' ) . '/path/to/script.js' );
}
add_action( 'wp_enqueue_scripts', 'wpa_65602_enqueue_scripts' );