To install Apache and PHP5 on Ubuntu, you will first need to make sure that the restricted repositories are enabled. You will want to edit /etc/apt/sources.list and make sure the following lines are in it and are not commented out with a #. If they are commented out, you will just need to remove the # character.
deb http://us.archive.ubuntu.com/ubuntu/ natty multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ natty multiverse
deb http://us.archive.ubuntu.com/ubuntu/ natty-updates multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ natty-updates multiverse
deb http://security.ubuntu.com/ubuntu natty-security main restricted
deb-src http://security.ubuntu.com/ubuntu natty-security main restricted
deb http://security.ubuntu.com/ubuntu natty-security universe
deb-src http://security.ubuntu.com/ubuntu natty-security universe
deb http://security.ubuntu.com/ubuntu natty-security multiverse
deb-src http://security.ubuntu.com/ubuntu natty-security multiverse
Once that is done, you will want to run this command to update all of your repositories.
sudo apt-get update
Then we can start installing Apache and PHP. First we want to install Apache:
sudo apt-get install apache2
Then PHP5:
sudo apt-get install php5
We will also need the module to allow Apache to run PHP.
sudo apt-get install libapache2-mod-php5
After that, everything is done, we just need to restart apache to allow the module to load.
sudo /etc/init.d/apache2 restart
You can then verify that Apache is running by using the following command.
/etc/init.d/apache2 status
And also check PHP by running this command:
php -v
You should now have Apache and PHP up and running. The default document root for Apache2 is /var/www. You can begin putting your files there to be served to the internet.