You need to install skins to their respective folders in the "Paint Schemes" directory of your main IL2 folder.
Let's say you downloaded a Bf-109E skin. Typically skins are in a .zip or .rar archive, so you unzip them to "C:\Program Files\Ubisoft\IL-2 Sturmovik 1946\PaintSchemes\Skins\Bf-109E" and they will show up when you select them in the game.
"the Grumman Hellcat, unquestionably the most important Allied shipboard fighter of World War II" -Capt. Eric Brown, R.N.
complete edition is believe it or not, not the complete edition, they brought out a load of add ons after that and called it 1946, that is all the versions on one DVD.. quite cheap to buy these days then that would require 1 patch at the moment and another one shortly ( Beta is out)
If you want to fly online, most use 1946 but complete edition with all the add ons would work too, but thats an expensive way to get 1946
But yes if you download skins for different planes and you have the folders for those planes then unzipping them into those folders will give you those skins........