I know everything in C++ language tutorial and I am good enough at coding that I only review for reference. I want to learn more so I will be able to make meaningful coding contributions for an open source game project. What concepts do I learn to optimally code for an open source game community?
Well, if you truly know the tutorials that well, your pretty much there. To start, you'll need a graphics library. SFML (http://www.sfml-dev.org/ ) is a solid choice. Just start out making small things (like pong or whatever) and then gradually step up your production. As you program games, you will learn (mostly by searching and asking specific questions) many useful concepts that are most relevant to you.