You will need to provide a database for your drupal installation.  

This assumes you have some knowledge of MySQL, and already have it
installed and configured. If not, please refer to the Gentoo MySQL
guide at the following URL:

http://www.gentoo.org/doc/en/mysql-howto.xml 

Once you have a database ready all you need to do is to go to this 
location

http://${VHOST_HOSTNAME}/${VHOST_APPDIR}

and provide the credential required for the database access.

SECURITY NOTICE: If you use SSL on your Drupal installation, you
should enable the PHP configuration option 'session.cookie-secure'
to make it harder for attackers to sniff session cookies.

References:
CVE-2008-3661
http://www.php.net/manual/en/session.configuration.php#ini.session.cookie-secure
http://drupal.org/node/315703

After that you can start to use drupal.