How do I use my c/c++ libraries in D?

[Stan Hebben]

I have a lot of questions about using my c/c++ libraries in d.
- How does the compiler 'map' the c libraries to d modules? (ex. if I write
'import std.c.stdio', where does the compiler look for this file)
- Does the D compiler use C header files, or header files which are converted
to D?

I mainly want to use the Windows / DirectX API in D, as well as some other
libraries.

I suppose this question has been asked many times, but I couldn't find it on
the forums. (neither did I find my answer somewhere else on the web)