what is autoload in PHP?
This will be of help to you about usage of autoload. http://ditio.net/2008/11/13/php-autoload-best-practices/
It's a magic function that helps you include / require files using class name.
function __autoload($class_name)
{
require_once $DOCUMENT_ROOT . “/classes/” . $class_name .“.php”;
}
It's deprecated at PHP 7.2.0 and spl_autoload_register is recommended for that purpose.