Just dive in. Read everything you can. Experiment anywhere possible that you can afford to lose, and don’t be afraid to lose.
Once you learn how ESC’s, batteries, motors, video transmitters, GPS, basic RC functionality, auto pilot theory, and some programming works you’ll be well on your way.
Multirotors are nothing more than a collection of independent components that will function independently that are linked together to make an aircraft. We cannot understand the whole until we understand the individual parts. It takes legwork and time but visiting various high end manufacturers provides a lot of info. I’ll suggest some major RC manufacturers like Castle, Futaba, and KDE be added to the mix.