Addons in Garry's Mod

I recently purchased this off of Steam, and was wondering how to make addons work every time. People say to put it in the addons folder or just match up the files with the ones in your c drive, but it doesn't always work. Iread the Addons for Dummies thing, but it doesn't seem to always work. Mainly I just want to see if I can get this to work http://www.garrysmod.org/downloads/?a=view&id=14581 and any CSS addon to work (due to I don't have CSS.