Win32, select X86, X86_X64 and libraries for AMD64.
1) WIN32 system is WINDOW, whether 32-bit or 64-bit core is WIN32, why this is so, is historical.
In order to distinguish the Microsoft 32-bit and 64-bit, and the X86 X64 marked (32-bit system) so distinguished.
2) 64-bit system library.
This only shows the face of the 64-bit CPU, there are chances LINUX kernel. If WINDOWS, probably especially WINDOW 64-bit systems. But if the emergence of WIN32, WIN32 then this is referring to the X64_X86.
3) how AMD64 there is this?
Above have a, AMD64 is the face of a 64-bit CPU. So why not write X64 it. Some did so, some not, to consider whether the WIN32 only. INTEL 64 Why not call it, it is because AMD's 64-bit is raised.
Certain library provides WIN32, X86, AMD64-bit driver, you want to develop WIN64 bit you should choose which library?
WIN32, X86, ADM6? The answer should choose WIN32 (ie WINDOW 32-bit kernel == X64_X86)
Now all of the core will develop WINDOWS WIN32 API's.