Personally, I always recommend people avoid external libraries (i.e. SFML, SDL, OpenGL, etc.) when first learning C++. Why? Because it's a heck of a lot to take in at first, and if you don't have a good foundation to build on and decently understand the language you're writing in, learning a library isn't going to do you a whole lot of good.
So maybe take a step back and work on purely C++. Make console games. You might be surprised to see how this "restriction" might actually help you think creatively.
If your "C++ foundation" is already properly laid, however, think of the simplest game you can. Maybe tic-tac-toe or Pong, and try to recreate it (and keep it simple!). Try to program "properly," but also don't shoot for perfection, because I'll tell you right now your code will be far from perfect in many of your early (and even later) projects.