autoload.php

<?php
function autoloader($className) {
    $fileName = str_replace('\\', '/', $className) . '.php';
    //Try anove with only one backslash and note error code. Research this.
    $file = __DIR__ . '/../classes/' . $fileName;

    include $file;
}

spl_autoload_register('autoloader'); // Why is there a string here? Will it still work if I change it? How does this work?