Midi mapping to a controller is virtually automated in most DAWs. Most have a "midi learn" function that can easily associate a knob, button, or slider in the daw with a knob, button, or slider on a controller (a piano key is a button btw, and regular midi keyboard can be used as controllers) just by pressing, turning, or sliding the controller.

As for midi, its actually a really old and simple protocol. At base its hex that is interpreted as channel, note value, note on or note off (in midi there is no "sustain" per se, a note stay on until turned off and vice versa. That makes sense when you think of the bandwidth in the 80s. They couldn't have continuous data. Just discrete events.). There's other values, like velocity, but that's just the basic rubric.

https://ccrma.stanford.edu/~craig/articles/linuxmidi/misc/essenmidi.html