VSPackage Essentials
VSPackages are software modules that make up and extend Visual Studio with UI elements, services, projects, editors, and designers. VSPackages are the central architectural unit of Visual Studio. Visual Studio itself is written mostly as a collection of VSPackages.
To create a Visual Studio extensibility application, you first create a VSPackage. You can then add menu commands, tool windows, document windows, or other code to extend the Visual Studio IDE.
To use VSPackages, you need to install the Visual Studio SDK from Visual Studio 2013 SDK download.