Your server does not look like it has been correctly installed. Did you get any error when you installed Debian or apache2? If so, you should re-install Debian. If apache was the one with the error, you should do (assuming you are root):
apt-get update ## to make sure that you have the latest repository details
apt-get upgrade ## to make sure your server is up to date (no incompatibilities or other)
apt-get purge apache2 ## completely remove apache and any other config files related to it
apt-get install apache2 ## re-install apache
Then, you can edit your default configurations that are found in /etc/apache2/sites-enabled/000-default, using an editor. If the config file is still missing, look back at the installation logs, maybe there was a certain error that you have missed.