I've noticed that there is nothing about graphics in the tutorial.
That is because there is nothing about graphics in the C++ standard. "Graphics" are a concept that is implemented by the platform you working on. For example, Windows has GDI, DirectX and one or two other libraries to allow a developer to display an image. However neither of these libraries will work on Linux or Mac because in those cases the method for implementing graphics is completely different.
SHORT ANSWER: You need a library to write a graphical program. I recommend SFML: http://www.sfml-dev.org/
SFML is actually built on OpenGL so either way it's your choice. I'll say this though, most libraries for OpenGL are based on C so they take some patience to learn.
Even if you want to use OpenGL directly, SFML is a good choice because it gives you audio, window management, gamepad input, and it simplifies some OpenGL functionality (like texture loading).
If you want to learn OpenGL directly, I recommend this tutorial: