This guide is divided into 3 steps: installing/tesing Apache, PHP and finally MySQL.

Lets start with Apache:
1. Open the terminal (we will be using it through most of my guide) from Applications > Accessories > Terminal
2. Install apache2 using apt-get by typing the following

sudo apt-get install apache2
Note that you should know the root password.
Now everything should be downloaded and installed automatically.
To start/stop apache2 write:
sudo /etc/init.d/apache2 start
sudo /etc/init.d/apache2 stop
Your www folder should be in: /var/www/