If you're aiming to learn modern GPU api on Windows, I suggest starting with Direct3D 11. It does not have old historical baggage, its API is reasonably sane, and most concepts will easily map to newer d3d12 or Vulkan. Until you will write something that is CPU bottlenecked on submitting gpu commands, the d3d11 will have same performance as d3d12 or vulkan. Probably even better performance, because d3d11 is way easier to use.
If you want something simple just to get graphics on screen then OpenGL is fine too, but because of old compatibility stuff it might be very confusing which parts are good to use and which are not.
I have simple C code to get started with D3D11 here:
https://gist.github.com/mmozeiko/5e727f845db182d468a34d524508ad5f