If you are dining at the Poly that evening, then you drive right up to the resort gates and they will allow you in for your dinner - then you just stay for fireworks after until you are ready to go home.
If you are not dining at the Poly, but wish to use your own car, then you drive to MK parking, take the tram back to the TTC, and walk about three minutes to the Poly along the marked pathway. Reverse the process to get back to your car afterwards.
If you wish to use WDW transportation, then you take the resort bus from Pop to the MK, and from there you have a couple of options:
--Walk across to the Contemporary (5 minutes), take the monorail two stops up to the Poly and walk out to the beach (10 minutes, total of 15).
--Walk up to the front gates of the MK (3 minutes) and get on the resort launch (boat) to the GF/Poly (15 minutes, total of 18-20).
--Walk up to the front gates of the MK (3 minutes) and take the Resort Monorail line up three stops to the Poly (20ish minutes, total of 20-25).
--To get back to the buses afterwards, take either the monorail or the resort launch back to the gates of MK and walk to the last stop on the right side of the plaza.