Load FontAwesome by link and in WP

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.4.0/css/font-awesome.min.css" />

Or in a WordPress theme or plugin functions file:

function load_fontawesome(){
  wp_enqueue_style('fontawesome', 'https://maxcdn.bootstrapcdn.com/font-awesome/4.4.0/css/font-awesome.min.css');
}
add_action('wp_enqueue_scripts', 'load_fontawesome');

Usage:

<i class="fa fa-code"></i>

Output: