You can not create new apps that target Windows 8 in the VS2013 editions, only Windows 8.1.
Visual Studio 2013 Professional and above can be used to maintain existing Windows 8 applications, but Visual Studio Express 2013 does not have this capability. Rather, if you open a Windows 8 application in VS2013 Express you will be prompted to re-target
the application to 8.1 in order to work on it.
Compatibility information can be found on Microsoft's
Visual Studio 2013 Compatibility page.
Edit: Rob Caplan has created a
sticky forum post on this subject as well.
