Overview: Creating a Win32 DLL
A Win32 DLL is a binary file (written in C or C++ and using calls to the Win32 API rather than to MFC classes), that acts as a shared library of functions that can be used simultaneously by multiple applications.
Visual C++ will create workspace and project files for your program that you then add your own code to. There are two steps to this process. First, you use the Dynamic Link-Library icon to create new project files for your Win32 DLL. Next, you prepare your program for use by adding code to the source files created by the wizard (if any) or by adding source code files to the project.