Game Maker has a free version, a premium version and a trial version. The free version will not allow you to create an application that is for the Mac platform. If you would like to use the Game Maker Studio application for creating applications for the Mac then you need to download the Mac GameMaker development system before you can make applications for the Mac. You can download the Mac GameMaker development system from the Mac App Store if you don't have one yet.
There are many applications that you can create for the Mac platform. There are also many applications that you can make for the Windows platform, with many being freeware. There are several benefits to using the Windows application. First of all, you can customize your applications the way you want them to be, with many different aspects, such as the way the application looks, how it plays and what controls it has. This is not true when you are making an application for the Mac. However, you can create an application on the Mac that is nearly identical to the Windows application because they are both so similar to begin with.
Finally, the free version of the Game Maker Studio application will not let you download the Mac application. However, if you would like to download the Mac application then you can. However, if you would like to use the free version of the application, which does not allow you to download the Mac application, then you need to pay to download the Mac version. I would recommend that you use the free version of the Game Maker Studio application to learn and experiment with the different features and functions of the application.