The "Parking Aid" is the ultrasonic sensors in the bumper that cause a beep when you are getting close to something backing up. I would not have ordered them on a custom build, but they are present in some of the packages and happen to be on the truck I bought.
It beeps more rapidly as you get closer to something, also puts blocks of color up on the reverse camera screen. The problem is, anything at all on the back of the truck - tailgate down, camper, trailer - causes it to beep rapidly and loudly whenever reverse is selected. When it is beeping, Ford allows you to hit Down>OK and turn it off. But it comes back on again next time you start the truck because their lawyers have no nuts. If you have a trailer with electric brakes, the system senses their presence, and disables the Parking Aid. But that only covers some trailers: if you don't have brakes, or have surge brakes, or have electric-over-hydraulic brakes, or a camper, or the tailgate is down, the scheme does not work.
