OpenGL or “Open Graphics Library” can be consisder as an API library which provides a set of functions for manipulate graphics and images. However, OpenGL is actually a specification that specifies the result of each function should be or how it should perform.
Basically it is used to draw 2D/3D graphics by commanding to your graphics hardware (GPU) through its function.
Navigate to Prerequisites and CMakeLists to know what you will need and how to setup cmake.