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.
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.