Quote from ACCAkut :

You have to load it onto your lfsworld.net account first, then everyone downloads it automatically
Edit: Ups, oversaw last sentence.

Did you rename the skins after you uploaded them? They have to have the same name as the ones you use on your computer

Thanks for the help guys i accidentally renamed the file. It works now.

My custom skin shows up in the garage/pits on the car and everything but when I join the race it's not on the car. There is also a message saying, "skin:not found" then,"Your cars skin was not found at www.lfsworld.net", i did uplode it to the website before this message.