First things first, you shouldn't be using 11.04.
11.04 was only supported for 18 months, so it reached end of life in October last year. This means it hasn't had any security updates or bug-fixes for 6 months now and may well have security vulnerabilities that won't ever get patched, meaning it could be a trivial task for anyone to hack into your server and take it over.
The recomendation is to only use LTS releases for production servers, which means installing 12.04 as it has five years of support.
Once you have 12.04 you can install the entire LAMP stack (Linux, Apache, MySQL and PHP) with the following command...
This will configure Apache to server your website from the /var/www folder.
sudo apt-get install lamp-server^
For more information your first port of call should be the official documentation...