Modular Cars are great for transport of people, and even items. They feature many unique mechanics, one of which is how modular they are.

A single car 'chassis' can't be crafted, but found in the world randomly. These are most likely in a non-functional state, meaning you'll have to repair them yourself by finding the parts inside blue boxes. This is currently the only way to obtain the chassis for these cars, and by extention owning one.

The thing you're probably wondering is how to modify them. Well, I'm glad you asked: There are multiple modules that can be reaserched for scrap, and these can be put onto the chassis of a car. Depending on the type of chassis, you may only be able to fit 2-4 modules on it. Small has only two modules, medium has three, and large has four. The many different modules are separated into different catagories:

Cockpit modules:

Armored cockpit module; Cockpit module; Cockpit with engine module

Passanger modules:

Armored passanger module: two-seater module: six-seater module

Storage modules:

Liquid tank module: Storage module

Engine modules:

Engine module