Question about Pioneer DMH-A240DAB

No, the device doesn't have a navigation system; the devices with navigation systems are in a completely different league in terms of price - unfortunately.

I can't say at the moment whether it fits a Golf. I installed mine in a Honda Jazz and had to replace the entire upper centre console with another one with a matching ISO slot; it wasn't too much of a hassle, not even financially. What is expensive, however, is the matching CAN adapter so that you can still operate the unit with the control buttons on the steering wheel. It cost almost the same as the radio itself.
There are many videos on the net on how to replace factory radios with ISO-compliant car radios.