Adding another email address to the autoresponder

I would like users to apply for a training course buy filling out a form, then I would like a notification to be sent to the user, the training company and the admin of the site.

What would be the best way to achive this, I have looked at this code but didnt understand it.

<?php
add_filter("gform_autoresponder_email", "change_notification_email", 10, 2);
function change_notification_email($email, $form){

    //applying notification routing to form Id 2
    if($form["id"] != 2)
        return $email;

    //creating email list from fields 2 and 3.
    return $_POST["input_2"] . "," . $_POST["input_3"];
}

?>

many thanks

thanks for your reply.

The site I am working allows training companies to create post of training courses they offer, the user can then book a course with the provider, so the 3rd address will be for the training company. This will differ as we'll have several different companies. I have set up a custom post with a custom field which they enter their email. I have also set up a hidden field on the form which gets populated with the email and that works fine.

I just need to somehow get the email to be copied and sent to the training company email as well as notifications to the user and admin.

many thanks