Excerpts from site:

This tutorial attempts to get you started developing with the Win32 API as quickly and clearly as possible. It is meant to be read as a whole, so please read it from beginning to end before asking questions... most of them will probably be answered. Each section builds on the sections before it. I have also added some solutions to common errors in Appendix A. If you ask me a question that is answered on this page, you will look very silly.

What this tutorial is all about
This tutorial is intended to present to you the basics (and common extras) of writing programs using the Win32 API. The language used is C, most C++ compilers will compile it as well. As a matter of fact, most of the information is applicable to any language that can access the API, inlcuding Java, Assembly and Visual Basic. I will not however present any code relating to these languages and you're on your own in that regard, but several people have previously used this document in said languages with quite a bit of success.

This tutorial will not teach you the C language, nor will it tell you how to run your perticular compiler (Borland C++, Visual C++, LCC-Win32, etc...) I will however take a few moments in the appendix to provide some notes on using the compilers I have knowledge of.

If you don't know what a macro or a typedef are, or how a switch() statement works, then turn back now and read a good book or tutorial on the C language