I didn’t write the documentation, but I think it’s excellent. It does answer your question about retrieving monitors (see the links in the section I referred you too).
To draw to different windows you need to understand OpenGL contexts, which is part of the OpenGL API. The GLFW API provides the function glfwMakeContextCurrent for switching contexts. Context sharing provides the requried functionality for sharing buffers, see the OpenGL docs on this and the GLFW one I referred you too on setting up a shared context.