Certain things just can't be done in pure .NET, and the developer has to drill down to the Windows API. This is achieved through .NET's Platform Invoke (PInvoke) functionality, which requires declarations to be supplied by the developer.
Manually defining and using PInvoke signatures is an error-prone process that can introduce extremely subtle bugs. PInvoke.net supplies you with tried and tested signatures and type definitions, so that you don't have to spend time writing them from scratch.
Download the PInvoke.net add-in for Visual Studio and save yourself the effort of having to open up a web browser to search for the PInvoke.net website. You can now insert a PInvoke signature with the click of a button while you're working on your application in Visual Studio.