I don't see any encoder info up there - looks like you forgot to post it? In terms of the motor - it looks like the manufacturer has a lot of data - which is always a good sign.
You might want to read this introductory info about encoders here:http://www.robotappstore.com/Robopedia/Rotary-Encoder
It goes over how some rotary encoders work - which could help you out. Generally, most quadrature encoders have two channels (A and B). You could either poll the pins, or better (if you have the option) I would recommend using interrupts tied to your pin state change. A brief blurb about interrupts can be read here:http://www.robotappstore.com/Robopedia/Interrupt
Hope this helps, and if you have any questions feel free to let me know!