You have two options:
- Buy a prebuilt unit like StreetDeck.
- Learn how to build a PC from components.
A vehicle computer is just like another computer with a few significant differences:
1) It neds to run off 12v DC power in teh car instead of 110v (220v in Europe) in your home.
2) It needs to be small enough to fit in your vehicle.
3) It needs accomodations for potential climate extremes (extreme cold in Minnesota, extreme heat in Dallas, for example)