Start by finding a hands-on course or organize an elective or fellowship. No one learns to drive a car by reading a book, listening to didactic lectures or watching YouTube videos. Getting your hands on the probe early with a trainer next to you on a real human subject will orientate you to probe handling and hand-eye-screen coordination. This will give you a basic grounding.

Next find a good book or online resource with videos starting with the basics and building up. Aim to practice regularly what you are learning from reading and watching the videos on real subjects.