ok im a noob, so can you tell me how to install a skin??? please thankyou

Im afraid, you cant do that as a demo racer.

The other drivers wouldnt be able to see your skin anyway, because there is no automatic skin download in the demo.

You can put a skin on your own car by putting the skin into the data/skins folder, but as my esteemed colleague says ... nobody else will see it unless you come S2 racing with us

You can put a skin on your car if it's a valid jpg image and placed inside the data/skins folder.
In the garage/pits, click "new colors" on the left, and then in the horizontal menu at the bottom of the screen, there is a tab "colors" - click this, and a small button on the bottom will show up, with the name of the currently loaded skin. Click it, and finally chose your skin in the list that will show up, in order to assign it to the currently loaded color setting (the one you created on the left at the beginning). This color file is named *.col and will be saved in the data/settings folder

If you want other racers to see your skin online, you have to either make them download the skin manually (which requires you to upload it somehwere), or buy the S2 license, which allows you - besides hundreds of other cool features - to upload the skin onto the LFS server, and people who see your car, will automatically download your skin and be able to see it. The skin upload (S2 licensed only) can be found here: http://www.lfsworld.net/?win=skins

Downloaded skins will be saved in the skins_x folder and might not be modified or used, depending on what the respective owner / author of the skin says. It's always a good idea to ask the creator of a skin because messing around with it can cause trouble.