1.Choose the car you want. Here, I will take as an example my Porsche 911 GT1 Strassenversion.
After importing the car, just go to Surface>Mapping>Edit UV and choose the body. Mark only the options of the screenshot.
Well, after this, open Photoshop and put the mapping, and put your vinyls any way you want looking to the UV-Mapping to place the vinyl better.
Now just give wings to your imagination!