Is this page controller right?

Hi. A few weeks a go i’ve opened a post here where I asked why i get a error when someone sign up on this website. kibsstudio.it
The person that made this website disappeared and i can’t understand at 100% how he made it.
I think that the error that people get comes from a bad configuration of the Controller page. Do you think is something wrong on this code? Could you actually help me to understand how to create a new sign up form? thank you

<?php

class AreaRiservata extends Page

{

private static $db = array(

    'TitoloSeo' => 'Text',

    'DescSeo' => 'Text'



);



private static $default_child = "AreaRiservataFile";

private static $allowed_children = array("AreaRiservataFile","SuccessAr");







private static $has_one = array(



);



function getCMSFields() {



    $fields = parent::getCMSFields();



$fields->addFieldToTab("Root.SEO", new TextAreaField('TitoloSeo', 'Titolo Seo (Max 70 caratteri compresi di punteggiatura)'));

$fields->addFieldToTab("Root.SEO", new TextAreaField('DescSeo', 'Descrizione Seo (Max 160 caratteri compresi di punteggiatura)'));



return $fields;

}

}

class AreaRiservata_Controller extends ContentController

{

private static $allowed_actions = array(

    'login', 'FileDl'

);



function ChildrenArearis(){

    $newlist = AreaRiservataFile::get();

    return $newlist;

}



public function FileDl() {

    global $databaseConfig, $databaseConfigExt;

    DB::connect($databaseConfigExt);



    $username = $_POST['username'];

    $surname = $_POST['surname'];

    $filetitle = $_POST['filetitle'];

    $filename = $_POST['filename'];

    $datadownload = $_POST['datadownload'];

    $email = $_POST['email'];



    $insert = SQLInsert::create('"filsedl"');



    $insert->addRows(array(

        array('"ID"' => "", '"username"' => $username, '"surname"' => $surname, '"filetitle"' => $filetitle, '"filename"' => $filename, '"datadownload"' => $datadownload, '"email"' => $email)

    ));



    $insert->execute();



}

}