I'm quite surprised that nobody has suggested Crash Course. The first one they did - Crash Course World History by John Green - is really great, and I personally found both endearing and funny (https://www.youtube.com/watch?v=Yocja_N5s1I&list=PLBDA2E52FB...). It's not advanced material, mostly high-school level, but you've got to crawl before you can walk, and it can help to fill in some missing spots if you have them, or give a high-level overview or recap in an entertaining way. Example: I'd done basic biology, but taken instead chemistry and physics (where I was, you only did all three if you wanted to go into medicine). I used Crash Course Biology (https://www.youtube.com/watch?v=QnQe0xW_JY4&list=PL3EED4C1D6...) to back-fill my knowledge before studying a masters in Bioinformatics.