GPIO pins can only supply a limited amount of current, so it's often necessary to use some interfacing circuitry to boost the current if you want to power things like motors and lights. The Pi Face board is designed to make interfacing easy.
Before you can use a Pi Face, you need to enable your Raspberry Pi's SPI driver. You can do this by opening /etc/modprobe.d/raspi-blacklist.conf, and insert a '#' at the start of the line that says 'blacklist spibcm2708'. Save the file (you'll need to open it as root in order to be able to save it).
Next, you need to install the Pi Face libraries with these commands:
$ sudo apt-get update
$ wget http://pi.cs.man.ac.uk/download/install.txt
$ chmod +x install.txt
When you've installed the software, shutdown your Pi and disconnect it from the power supply. Carefully attach the Pi Face board making sure to line up the pins correctly correctly before pushing them into th Pi Face socket. Then boot your Pi and run the Pi Face emulator with this command:
You can still use the wiringPi GPIO utility but if you use it with a Pi Face, you need to use the -p option. Note that when an output is enabled, an LED will light up.