The leds are wired in a common-cathode configuration. Each one has its anode connected to a different digital pin, and the cathodes are all wired together. This common cathode is then connected to a single 330 ohm resistor that is wired to the arduino's ground. You may need to adjust the resistor value for your leds. You may get more consistent brightness by giving each led its own resistor (so none of the leds are wired to each each other), but I didn't see a difference with mine, and it made the wiring a lot easier.
The button on pin 2 activates an interrupt to begin displaying the message.