Sample adding Javascript and CSS files to Wordpress

add_scripts_to_wordpress_theme.php

function wp_add_javascripts() {
    wp_enqueue_script('utils-js', 
get_stylesheet_directory().'/assets/js/utils.js', array('jquery'),'1.1', true);
}

function wp_add_styles() {
    wp_enqueue_style('utils-css', 
get_stylesheet_directory().'/assets/css/utils.css');
}

//add to the wp_enqueue_scripts hook.
add_action( 'wp_enqueue_scripts', 'wp_add_javascripts' );  
add_action( 'wp_enqueue_scripts', 'wp_add_styles' );