Most (all?) top universities have free educational content, often including entire courses, available. For instance here [1] is MIT's open courseware site where you can download all the required media, including lecture video/notes/problem sets/exams/etc, for courses - completely for free.
Things like this are generally going to be orders of magnitude better than any YouTube video.
Sadly I disagree. Those resources are great but they don't come close to the visualization work 3Blue1Brown makes. Many subjects only clicked for me after watching his videos.
Things like this are generally going to be orders of magnitude better than any YouTube video.
[1] - https://ocw.mit.edu/