First you got to unzip it.
Then to find the defcon folder go to finder. In the task bar click go and it drops down a bunch of places to look hold down option. A new folder to open called "library" should appear click that. Then open "Application Support," Inside there you should be able to find defcon folder and in that folder is the folder for mods. Just drag the unzipped mod folder in there and you're good to go.
