i’ve also started but am not clued up in PHP. so i’ll try to help.
I’ll try and explain. Ray’s board uses a shift register to control the 8 valves. Go and read this to understand how a shift register works – http://bildr.org/2011/02/74hc595/
Now that i hope you know how it works, you’ll understand the 4 wires you have to connect from the Pi to the sprinkler board.
Also if you open his manual test program you will see his shift functions especially the shiftout one. etc
So using the PhpGpio module, we can talk to the pins like he talks to them in Python.
Hope this helps so far.