i just got photoshop (well the trial version) but how did u guys insert the background and all and i do need to make my pic a little bit smaller

Depends on what you mean by insert the background. If you're talking about putting your car in a different setting, I start with the car as a layer on top of a transparent background and erase everything around it by hand. You can then put that layer over top one of your design or another picture. You'll probably need to adjust color tones and lighting to make them match as well.

You can resize something by going to Image>Image Size at the top.