Good luck. That manual is not only the bare minimum in providing sufficient information, it is also seriously wrong, since they seem to have the RaspPi GPIO connector upside-down in the pictures. There is probably enough information there to get it talking, but I would find it confusing and ambiguous, and it is what I do for a day-job.
Forget I2C and SPI for the moment -- they add too much complexity. Use serial, and Python. You'll need to find the pyserial library, and you'll need to find out how to free up the serial port. And don't follow the pictures because they are wrong. The pin numbers in the tables look right.