1 Go to layer 2, go around the lines with lasso tool, then fill
with any colour of choice.

2 Once the basic colour has been confirmed, it is then time to
concentrate on building up detail. Examples of detail, would be the
lighter edges on the top halves, shading in the bottom areas etc etc. I
shall show you first how to make the arches the arches above look as
though they come away from the bodywork, and curve around. This is simply
done, using the following steps:
First
lasso around the indicated areas
Select a slightly lighter colour (for lighter areas)
Select appropriately sized airbrush (indicated)
and brush around the TOP halves of the bumper (in this case)
Here's the same picture
after I've added lighter and darker areas for the shading.
It is a good idea to look at the original image to see where light and
darkness falls on the car, so that it can be followed through onto the
cartooned image.
This is all done using the lasso tool (as a mini mask) and the airbrush
tool. Other tools, such as the blur tool etc, can also be adopted for use
when cartooning.