WordPress enqueue scripts and styles

I using an open source WordPress theme and want to remove the styles and scripts from header.php file and write them properly. I’ve added the following code to my functions.php file and nothing happens.

function smarter_scripts() {

wp_enqueue_style( 'smarter-bootstrap', '//maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css' );
wp_enqueue_style( 'smarter-font-awesome', '//cdnjs.cloudflare.com/ajax/libs/font-awesome/4.4.0/css/font-awesome.min.css' );
wp_enqueue_style( 'smarter-google-fonts-open-sans', '//fonts.googleapis.com/css?family=Open+Sans:600,400,300,700' );
wp_enqueue_style( 'smarter-google-fonts-josefin', '//fonts.googleapis.com/css?family=Josefin+Sans:400,600' );
wp_enqueue_style( 'smarter-style', get_template_directory_uri(). '/style.css' );

if (!is_admin()) {
// comment out the next two lines to load the local copy of jQuery
//wp_deregister_script('jquery'); 
//wp_register_script('jquery', 'https://ajax.googleapis.com/ajax/libs/jquery/1.11.2/jquery.min.js', false, '1.11.2'); 
wp_enqueue_script('jquery');    
}
// load a JS file from my theme: js/theme.js
wp_enqueue_script('smarter_script', get_template_directory_uri() . '/js/script.js', array('jquery'), '1.0', true);
wp_enqueue_script( 'smarter-bootstrap','//maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js', array( 'jquery' ),  true );
}
add_action( 'wp_enqueue_scripts', 'smarter_scripts' );

Also, I can’t figure out why when I add plugins, the CSS and JS files do not automatically load in the theme. I have to manually add the files to the header.php or footer.php files in order for the plugins to work. Does anyone know why this happens? (I am not a theme developer but I’m trying to fix a theme that my company is using.)

Reference:

WordPress: Loading multiple scripts with enqueue