Fargo Billiards
This channel has been around for a while, and has about a dozen great videos that explain the fundamentals of pool. It also has some indepth videos on how player handicaps are determined.
Channel Link: youtube.com/user/FargoBilliards
Dr. Dave Billiards
Videos from a PBIA Master Instructor and published author. His book The Illustrated Principles of Pool and Billiards is a must have for any library. He is also famous for his instructional in-person boot camps.
Channel Link: youtube.com/c/DrDaveBilliards
Tor Lowry
Learn from detailed instructional pool videos on topics from controlling your cue ball positioning, to offensive and defensive strategies for every game in pocket billiards. He even has great videos on how to use English (also known as Spin) successfully.
Channel Link: youtube.com/c/TorLowry
Pool School
In depth discussions and examples on taking your pool game to the next level. If you are looking to improve the way you think of a run out, this channels videos are a must watch.
Channel Link: youtube.com/c/PoolSchool
Niels Feijen
If you are looking for instructional videos from someone who has a history of doing well in tournaments, then this is a great channel. Niels walks you through his way of thinking at the table and provides a ton of advice to improve your game.
Channel Link: youtube.com/c/NielsTheTerminatorFeijen