I am using a wordpress child theme and have added css code to the style.css and everything works well. When i want to add function to my function.php file I always get error message. I am new to using the child theme so my problem is to know where to place functions. Should all new functions be placed inside funtion.php or does it depend on each function.

function.php file:

<?php
add_action( 'wp_enqueue_scripts', 'my_theme_enqueue_styles' );
function my_theme_enqueue_styles() {

    $parent_style = 'PRANAYAMA_YOGA_THEME_VERSION'; // 

    wp_enqueue_style( $parent_style, get_template_directory_uri() . '/style.css' );
    wp_enqueue_style( 'child-style',
        get_stylesheet_directory_uri() . '/style.css',
        array( $parent_style ),
        wp_get_theme()->get('Version')
    );
}

For example i tried to add a onepage-nav function to my Menu, like this

  $('#nav').onePageNav({
    currentClass: 'current',
    changeHash: false,
    scrollSpeed: 750
  });
 /

But my site crashed.

Thanks in Advance