The educational strength of YouTube is variety. You can compare three explanations of the same theorem, hear a teacher from another country, and rewind a sentence until it settles. No single lecture has to be the only voice.
The weakness is the same variety. Autoplay will happily replace a lesson with a distraction. The useful habit is to treat the player like a workshop: pause, try the step, come back to the exact chapter.
Notes turn watching into studying. Write the command, the measurement, or the verb tense. If you only listen, the video is background. If you copy the move, it becomes practice.
Playlists help the next visit. Save a course in order, hide the videos you have finished, and keep one review list for the parts that still slip. Search again only when you need a better teacher, not because you lost your place.
Used this way, YouTube is a pocket classroom that stays open after midnight. Used the other way, it is a window that never asks you to pick up the tool.