You use the subset of .Net Framework called .Net for Windows Store apps to bring C# functionality to Windows Runtime.
Windows Runtime (WinRT) is unmanaged, but C# is managed, how?
You use .Net for Windows Store apps types along with WinRT types and during execution .Net will interop with unmanaged WinRT types.
.NET for Windows Store apps APIs[
^] shows types supported by .Net subset that you use alongside with unmanaged WinRT types.
So it is not only types you have by C#)
You can use any unamanged WinRT type by C# in this way.