Add javascript to WordPress

using $ instead of jquery in wordpress
including-jquery-in-wordpress-the-right-way/
javascript-for-wordpress-people
http://royemory.com/javascript-resources/
custom-jquery-plugin
jquery & ajax
wp_enqueue_script
YouTube:
Adding a JavaScript File to WP #7
Adding A JavaScript File to WP #8

Use an anonymous function to run jquery
(function($)
// $ Works! You can test it with next line if you like
// console.log($);
})( jQuery );

in child theme function.php, insert a php function to enqueue the script.

function twentyfourteen_child_scripts() {
wp_enqueue_scripts( 'extra js', get_stylesheet_directory_uri() . '/js/extra.js');
}
add_action( 'wp_enqueue_scripts', 'twentyfourteen_child_scripts' );