You will need Photoshop or Gimp.
I use Gimp BUT THIS APPLIES TO BOTH.
You will need to name the Skin for example Douglas Bader Hurricane.jpg(this has to be a 2048 x 2048 .jpg file) then select File then Save As (for Gimp 2.6)
or Export As(for Gimp 2.8.)
Once you have made your skin you will have save it to for example \Users\.......\Documents\1C SoftClub\il-2 sturmovik cliffs of dover\PaintSchemes\Skins\Hurricane
Then view the skin in the PLANE section of main menu.
To get you started I have included a link to Layered Templates that I have made.
Good Luck
Keith
http://forum.1cpublishing.eu/showthread.php?t=190093