Hello guys, i want to say it in 3 steps:
First, find a good picture from a car, like this here:
Later, Brush the full car with 1 color (what you want to your car), then make some things like windows, tyres etc with black..why black? couse u won't use it just at the end:)
the third step is making the car reflections, just copy the things from your background, and put them to the right position:)
this is just a quick tutorial, if you would continue, you will need so much practise, and you will have your own style aswell
i will post a pic from this car when it will be done