Scratch modeling an actual vehicle is extremely difficult, and although I have never tried, I wouldn't recommend scratch modeling an entire car it would probably take months or more. To scratch model a vehicle though or parts I would recommend 3DS or SketchUp, or if it is very basic ZM3, and to actual build a vehicle like putting the lights on it etc. then you would need to use Zmodeler3. There are not many tutorials out there on ZM3 although I may try to make some simple ones in the future, but it isn't really possible to make a general tutorial for ZM3, as there are SO many issues you will run into, and different fixes/solves for each of them, and they all depend on certain things. What I did was I started trying by myself and when I came into a specific problem I would ask someone or look it up as there are a few answers to specific questions, but a general tutorial would be very hard to do. If you literally have no idea how to start I would say just start with merging your base model on and then figure out what you want to make (go with something basic, like a slicktop car or something) then figure out if you want to do the interior first, and lets say you start with the console. Then you ask someone what you should do from there etc. Let me know if you have any specific questions and I will try my best to help you :)
https://www.zmodeler3.com/
You need to purchase a subscription to ZM3 so I would recommend going month by month because it is easy to lose motivation in like a week and you dont want to waste all that money.