I believe this has been told before, but I'll tell you anyway. You just have to download the correct file. It depends if you have AUS or not. Then, use 7zip, WINZIP, or WINRAR to extract the .rar file. The new folders will appear in, well... wherever you extracted the file. They'll include Prototypes, Scripts, etc. Then, just copy and paste them in your LA MOD folder and allow all overwrites. After that, just play!