Crash Course is a YouTube channel run by Hank and John Green. John Green is a famous author, most well known for his novel The Fault in Our Stars. I began watching Crash Course almost since the very beginning with their first series on world history. The first video I watched was Mesopotamia: Crash Course World History #3. Since then they have covered topics such as Biology, Chemistry, U.S. History, and Literature. They have also branched out with more presenters to cover topics such as Astronomy, Economics, and Physics.
The topics are presented at about the high school level, and in some cases roughly correspond to the associated AP classes. I do not watch all the shows, there are some topics that I enjoy more than others (history), and some that I can't watch because, well, I teach it (physics) and I go, "Oh, yeah that. Skip!". But for people who are just learning it, they present a good introduction, while also being engaging and interesting.
There is some high school level humor in some of the shows, but that should be expected. I recommend this for high schoolers or for anyone who wants a good introduction to a particular topic.