Depends upon what info you are after. For windsurfing most of us use KA72 (www dot ka72 dot com). Logs speeds, kms, time and maps to google maps
Doesn't matter if Apple or PC as it is internet based software. Set yourself up with a free log in and get started. Take out your card from the GT31 and throw it in your card slot in your apple and select the file to upload once you enter KA72.