We're almost done, there's just a couple more things to do before you can try out your new mod!
Firstly we must turn your folders with the files inside into a .vpk file so that the game can read and make use of what you've just made. To do this we'll need a special program which I like to call the "VPK Maker". You can find this tool in Steam/Steamapps/Common/Left 4 Dead 2/Bin/
In this "bin" folder you'll see a lot of files, and the one we're looking for is called "vpk" which is an application file. Locate this file and then right click it, and select "Create Shortcut".
This should have created a shortcut to this application in that same folder, now simply drag the shortcut (not the vpk app) onto your dekstop.
Before the next little step it's important to give your mod/ addon a name so that you can locate it in the game. This is very simple to do. Create a Notepad document (.txt). Use this as a template
addontitle "[Insert name here]"
addonauthor "[Insert name here]"
addonDescription "[Insert description here]"
Copy everything above and insert it into the notepad document, replacing [insert here] with the names of your item / author. Once done save the document as "addoninfo" (all lower case letters without the speech marks) Place this .txt notepad file inside your first file with the materials folder, which in this case is "M16 Arctic Camo" Below is a screenshot of what it should look like.
We're almost done. Now that folder I named "M16 Arctic Camo" is what we're going to turn into a .vpk file. Simply drag the folder and place it over the top of the vpk shortcut file. This will turn your folder into a vpk (and keep your original folder). It should look like this.
Now you have the .vpk file and it's named correctly, it's time to add it to the game. Go to Steam/Steamapps/Common/Left 4 Dead 2/ Left 4 Dead 2/Addons
and place your new VPK file here.