Alexander Kent wrote his second article for The Code Project demonstrating the usage of Platform Invoke Services in Visual C# to interoperate with Windows Media Player.
In short, Windows APIs are DLLs that are embedded in the Microsoft Windows operating system. The advantage of using Windows APIs in your code is that development time and complexity may be reduced because they contain hundreds of useful functions already written. The disadvantage is that Windows APIs do not use managed code and have data types that are different from those used with Visual Studio .NET. While the .NET framework has wrapped a significant portion of the Win32 API into managed code, the ones that remain unmanaged and without a .NET equivalent may be called by managed code using the platform invoke service.