If you don't have a skins folder, just create it, and make sure the steklo_x3 and steklo_x3fmc folder inside the 7z file is placed directly inside the skins folder, and not a subfolder of it.
If you've got a previous version, go back to the default skin, then delete the old steklo_x3 folders before installing the new version
Go this post and download the mod.
If you want to put this file on another website. Please link to this page, but DO NOT under any circumstances rehost this file on your own servers.