Microsoft has a tutorial on how to build a Windows 8 app located here:

Before you start, I want to let you know 2 things:

1) This is a tutorial for the Windows 8 operating system, not Windows Phone 8 operating system.

2) Steps 1 through 4 require that you use Visual Studio 2013 on Windows 8.1. Step 5 requires you to use Visual Studio 2012 with Windows 8.