Okay if you're serious about skin creation you need a graphics editing program that supports layers (photoshop, paintshop pro, gimp, etc).
Then you need to download and install the hi-res pack and set your textures to 1024. Then you need to go into the hangar and right click on a plane and "save default skin".
You need to work in 1024, and if you don't have the hi-res pack installed it defaults out at 512 (even if you set it to 1024) to save space on downloads. So you need hi-res to get the proper template.
Then you go to the skins directory, open the name of the plane you saved, get the files you need (just ones that show wings or fuselage, don't need all the instruments) and you "paint" over them. Use layers so you don't permanently ruin what's on the default. Use layers to paint the colors, the camo, the whatever, then the details, the panel lines, the dirt, the weathering, and that's a highly simplified version of what you need to do.