Win32Ada is a binding for the Microsoft Win32 API. This binding can be easily installed from the provided installer. To use the Win32Ada binding you need to use a project file, and adding a single with_clause will give you full access to the Win32Ada binding sources and ensure that the proper libraries are passed to the linker.
with "win32ada"; project P is for Sources use ...; end P;
To build the application you just need to call gprbuild for the application's project, here p.gpr: