First let us start with the “Windows SDK” (Software Development Kit) which is designed to create Windows applications. It consists of large set of functions, messages, structures, macros and resources. It is a set of tools designed to help C programmers create Windows applications.
Windows SDK consists of the large set of books describing functions, messages, structures, macros and resources. There are also tools including a dialog editor and an image editor, on-line help files and a set of windows libraries and header files.
It has large collection of API (Application Programming Interface) functions written in C. The API is a set of functions that are part of Windows Operating System. Programs can be created by calling the functions present in the API. One doesn’t have to bother about the internal working of the functions – just knowing the function prototype (name, arguments) and return value one can invoke the API functions. A good understanding of the Windows API will help you to become a good Windows programmer . Windows itself uses the API to perform its GUI magic.