Please download s2container.php-version.tar.gz and unpack it. The following directory will be created.

s2container.php/
  +-- classes/
  +-- example/
  +-- sbin/
  +-- test/
  +-- Apache_Software_License_2.0.txt
  +-- S2Container.php
  +-- S2ContainerCore.php

Please require "S2Container.php", then it becomes usable.

<?php
require_once('/path/to/s2container.php/S2Container.php');
?>