There's a couple components under the LED matrix. It's a pretty easy assembly. Check the "description" for a link on finding pin 1. New versions of the kit use the MAX7219EWG which is a 24pin Wide SO, and the whole board is hidden behind the LED matrix, making it easier to orient them in different directions or even a grid (they also use SMD components so you're only soldering headers).

I soldered the header pins backwards and "inwards" so I could hide the other board behind it.