Nonce help needed

I created a form that pulls data from a database. The fields fill in fine. I want to protect the form by making sure the user is at least an Editor so I added:

if(current_user_can('manage_options') && (strlen($_GET['PID']) <= 5)){
    $auth = 1;
}
else {
    header('Location: top of the site being protected');
    exit;
}

So I included the WordPress blog header before the above code:

define('WP_USE_THEMES', false);
    require_once( 'wp-blog-header.php' );

That worked fine but then when I submit the form after edits – I get an error: “Security check: referal does not match this site.” After reading a bit I learned this has to do with nonces. I’m not sure why/how to deal with it and can’t find a way to troubleshoot the issue. I’d appreciate if someone could point me in the right direction.