I struggle to give a sensible answer to that question, because I think that including GPS in the PPL would make everybody realise what a load of useless cr*p they have been taught the previous X hours. I really do think that is the biggest reason PPL instructors don't want this; it would undermine so much of their whole approach to flight training.
But anyway....
Mandatory moving map (anything less is just too difficult and dangerous)
How to switch it on.
The general principles of loading a route (a "flight plan") into it, checking that it looks right, and flying it by adjusting the heading to make the aircraft's track match the flight plan leg track.