First, obviously you need a vehicle, it does`nt matter as long as it has atleast 1 wheel capable of turning and 1 wheel capable of moving the vehicle, Also it is recommended that the vehicle has a battery and a steering wheel. If not, i recommend you find a better vehicle.

This is 100% optional, you dont need to get spare parts, but i recommend you do so if a naked 5 years old decides to break its tires. But as you see, even with 2 tires you are still good to go.

Simply add parts to your vehicle that make it either look better but dont do much, or add parts to it that are useful and give you the advantage.

Obviously you have to test the vehicle on the most defenseless creature you can encounter in unturned, the Fresh spawn. Simply drive towards them and make sure you hear that "Splatt" sound and blood splatters, if you dont see a dead fresh spawn, find a new one and try again.

Here is a good example of a vehicle.

Congratulations, you have a working vehicle that is useful to you with some other way than running over fresh spawns and moving around faster.