check your header.php it should contain <?php wp_head(); ?> before the closing </head> tag.
check your footer.php it should contain <?php wp_footer(); ?> before the closing </body> tag.
You also need to hook your function to wp_enqueue_scripts action hook and then add wp_enqueue_script() and wp_enqueue_style() inside that function. e.g;
function add_theme_scripts_styles() {
wp_enqueue_style( 'style-name', 'path_to_the_style.css' );
wp_enqueue_script( 'script-name', 'path_to_the_script.js', array('jquery'), '1.0.0', true );
}
add_action( 'wp_enqueue_scripts', 'add_theme_scripts_styles' );