this is a multilayered skin overlay with rust, dirt and oil to make the Bf-109 look more weathered.
For this mod I expect, that you are able to handle liveries and you do have Photoshop or any equivalent software, which can process psd-files. Otherwise you may have problems to put it into a Bf-109 skin.
Redistribution is unlimited, because I would like to see more new skins wearing this stuff :-)
To avoid crossing the 100MB limit, I zipped it in rar5, so maybe WinRAR or 7zip will say that the archive is corrupted, which is wrong. You just need a to update your unzipper.