Now that we have the wifi setup, we are going to download and install the necessary software to our pi. Since our usb port is now being used by the wifi dongle, we will do this via ssh.
If you are using Ubuntu, open up the terminal and type ssh pi@[Your Pi's Ip address]. If you are using Windows, you can download Putty. On OSX, you can also just ssh from the terminal. Again, the default password on Wheezy is raspberry.
Once your a logged in, download, compile, and install Wiring Pi. This software allows us to control the GPIO pins on the pi. Here is a step by step guide for that:http://wiringpi.com/download-and-install/
Once Wiring Pi is installed, you will want to install Apache and PHP via these commands:
$ sudo apt-get update
$ sudo apt-get install apache2 php5 libapache2-mod-php5
Once this is done, you will have a working webserver! To verify that, just type in your pi's ip adress in a browser. You should see Apache's default website which says "It Works!".