First. There are a whole lot of skinners that do work that puts me to shame. I do real basic stuff, don't know the advanced tricks. Many people have been asking "How do you make a skin ??" This is a very basic example just to give you an idea of what's involved in the skinning process. I prolly do stuff ass-backwards but it works for me. Adobe Photoshop is the tool. Nothing beats Adobe for what it can do.
Every thing is done in layers, every layer has a name and layers vary in transparency from one to the next.
My first project is a P47D-25 belonging to Col. David Schilling of the 56th fighter group. ( still in the works )

IL-2 has a beautiful skin done of the plane so I was able to take the colors samples and the rivits along with the paint "pattern" from that skin.
You start with the basic skin in AH.

Change image size to 1024. Changing the lightness and contrast so that you have a good view of the panel lines already in place.
In the Osprey book on the 56th they have a page with panel lines. Scanned those and put them in PS. Blowing the original lines up to 1024 makes them huge. Option one is to retrace all the ones from the game or Option two, use a scan of Osprey and shrink them down and adjust them.

Then I laid the panel lines over the games original and transformed the size and scale until they match. ( Checking ingame )
Rivits are next. You can spend DAYS on rivits, copying, offsetting in a different color, and on and on. Mine are dots.

Now you have two options, you can make your own
Or you can fudge and use someone elses if available. I fudged. I used the rivits from the IL-2 skin. Laying the rivits over the panel lines ( which are correct ) transform scale etc until they are correct ( Checking ingame )
When your finished with one wing, you transpose horizontally and match up everything for the other wing.
Now I can paint. Using the panel lines and rivits as a reference point along with historical photos etc.

As you can see the paints are all one color, real paint on a used beat up warbird doesn't look like that. Now it's time to make it dirty, beat up and faded. Next layer I call the mottled layer.

Looks like hell. But when you drop the transparency down to 3-6% it gives the paint a real look, it's no longer all the same.
Now add some dirt and stuff using transparency for the right look.

Add some paint chips..

Now give it an overspray of a dirt color. Works as a highlight for the center part of the wing and adds a grimy look adjusting the transparency to taste. A dirt color sprayed from left to right ( ran out of image room on this post.. )
All of the layers can be adjusted in transparency to get "the" look your aiming at.
Insignias and lettering are all seperate layers so you can play with them to get them how you want them. I left those layers out of the example.
Finished product ( subject to alteration )

All the layers shown are in there in a certain order and at a varying transparency.. plus the insignias and painted lettering etc. Comes to twenty four layers for both top wings panels.
All images must be saved as an 8 bit 256 adaptive color bitmap ( tranposed in "mode" on the top menu bar ). Your "master layered PS" has to be saved BEFORE the bitmap transformation, or it get's reeeely ugly when you want to do some more work..
Being I'm slow and it's been awhile, that was about ten hours work for both top wings. If you figure in I ONLY have the top wings done, and still have the same process to do for the lower wings, Left and right fuse, top and bottom elevators you can be confident in the fact that you won't complete a skin in a weekend even if you don't sleep.
Then submit it for approval or revisions.
Cod help ya if you lose your layers..
Dat's da basics.
Lota fun, and a lotta work. It all comes down to the amount of "fiddle" that your up to. Cuz you can fiddle for bleams doin skins.
It's a model you build and paint in your moniter.