Hey, could you post the link of the channel you mean? Looking for 'shadertoy' in Youtube brought me only a playlist by 'The Art of Code'. Is that the channel you mean?
I've only only lightly dipped my toes into the webGL landscape, but I can definitely vouch for this man. I love the way he explains things. He's like the Carl Sagan of WebGL. I'll see if I can dig up a couple resources from my own foray drop them in this comment below.
https://www.youtube.com/watch?v=0ifChJ0nJfM is probably the the most beginner friendly.
https://thebookofshaders.com/ is another great place to start.
Good luck and enjoy!