Well, the old joystick connectors of a few decades ago aren’t actually midi. MIDI over USB is more normal today than the old 5-pin DIN standard MIDI connectors, as far as I can tell.
https://www.instructables.com/USB-MIDI-Controller/ is more likely to set you on a workable starting path.
I recommend this as a good free resource for learning circuits:
I’m not sure how much electronics design experience you have. It sounds like maybe not much yet. It’s not really something that you should expect to become fluent in jumping in trying to read complex circuit diagrams from the start. Like learning to read in the first place, you start simple and learn to recognize basic building blocks of circuits, and then as you see how they are combined you learn to recognize what they mean when you see them together.
But if you understand what some parts of the circuit do but not others, you could ask more specific questions.
I do find that when I have a specific question, I learn a lot reading electronics stackexchange posts from time to time: