The Plugin SDK is a C++ library that aims at making the development of plugins easier than using the raw OpenMfx API. For the reference of the underlying C API, see API Reference.
To get started with the SDK, it is recommended to follow the tutorial: the tutorial Getting started with the C++ SDK. At the bare minimum a plugin defines a subclass of MfxEffect and registers it using MfxRegister so these are good entry points for reading.
When using CMake, link your project to the target
OpenMfx::Sdk::Cpp::Plugin to use this SDK.