Redownload the full package. It appears you may have downloaded the upgrade release, which is fine, but if you are stuck you may want to start from scratch.
PHPBB Manual
http://www.phpbb.com/support/guide/
PHPBB Knowledge Base
http://www.phpbb.com/kb/article.php?article_id=271
Will get you started. If all else fails let me know and I will assist.