You dont use it to open the game, you use it to unpack the .rar file of the game.
Okay forget winrar then and try unarchiver. That should beable to extract rar files as well.
Here is an tut. video
How to Open Rar Files on Mac - YouTube
Make sure to redownload the mac version of the game just incase. extract the rar file and it should extract and .app file, double click it and it should start. I think, since macs make it way to confusing.