Thanks!!! I got it. I have again a question. If the car is a component now and I made some parts outside this componet and made them to component theirselves. Can I include this "out-components" into the "car-component" later?
PS: I'm really astonished about how much I can learn here in this forum, also such simple things! 
Hey, my second car is almost finished, only some details missing, but I have a problem. For example I make an exhaust as component and adjust it to car, then intersect with model. The polygons inside the exhaust can be cleared, but the stroke of the car's form are still in the exhaust. And if I erase them, the whole polygon disappear and a hole in the body of the car is the result. By Strg+Eraser the strokes don't disappear.
I hope it's understandable what I mean and somebody knows a solution... or doesn't any exists?
Hey, this is my first car I made with help of a tutorial. I made it to learn doing car models, so the shape and details weren't important to me. I made it because we have to design something in Art and I chose a car which I will start doing today.
This green "bucket" has also some mistakes, like the stroke in the side windows, which shouldn't happen for the real modell. It's also not rendered because it takes to long for a modell which is made to learn/out of fun.
A long story.. but here are the pictures... 
Thanks.
But I have some questions.
Is it somehow possible to make the rim and the hoop rounder?
And I think the colors look like made by Paint. How can I make it look "professionalier" ?
Powel
I know it's bad, but it's my first try. I made it after some minutes just playing around with SketchUp.
