Help with Building a Car

I have searched this and watched videos, but none that I have found seem to tell me how to build a car in the way that Roblox vehicles are build in the newer modular city template.

When I try to duplicate the constraints and welds of the orange car, into my little space buggy, it just bounces around then explodes.

Any help on how to do this, or a step by step guide or explanation on why you put the different constraints where they are, and what is their significance would really be appreciated.

Thanks