First of all, you must have Windows 8 OS installed on your machine - this cannot be the consumers preview addition.
Before stating to use the Windows 8 target platform you must have installed the Visual Studio Express 2012 SDK that supports building Windows Store Javascript applications (this can be found here). Once that is installed the values for these preferences should be automatically generated. If these values are incorrect or are not generated automatically for you, you should do the following:
- Make sure that the section titled VS2012 x64 Cross Tool points to the "vcvarsall.bat" in your MS Visual Studio installation. Without this you won’t be able to successfully create Windows Store packages.
- The WinJS API reference and WinJS Api Version need to match with the WinJS API that comes with your version of Visual Studio. To check this, create a blank Windows Store Javascript app in Visual Studio and, under References, right-click the Windows Library for JavaScript reference and select Properties. You should see an SDK Identity property that tells you all you need to correctly fill out these details.
You should also note that for GameMaker:Studio to generate your app correctly, you will need a Developer Key. Please refer to the section Global Game Settings - Windows 8 Tab: Installation.
Finally you should click on the Check Windows 8 SDK button to confirm that your selections are okay and that everything works as it should. If you get an error or you are not sure that your Developer Licence is correct, you may also click on the button labelled Acquire Developer Licence which will open up a command prompt and automatically go through the necessary steps to get you one.