Extract the content of the APP.ZIP file somewhere. Then, run the app file to start the game!
NB : You need to allow unidentified developers apps to be able to start the application. See this to know how to do it.
TROUBLESHOOTING :
If the extraction of the APP.ZIP file fails, try using another archive utility, such as "Stuffit Expander".
If you get a message saying the app cannot be run because it is from an unidentified developer, check this page.
In case of trouble, please send a message over the game forum.