Shadertoy for absolute beginners

Definitely bookmarked the article. I've been watching a playlist which is making shader programming click for me: ▶ this video "The Art of Code" channel, "ShaderToy Tutorials" playlist. I think if you know some geometry/trigonometry, once you wrap your head around writing a function that maps any pixel to a color (and how you add or multiply colors, and think in vectors), it starts to get fun. If you want a recommendation, I'd start with videos 30 and 37 in the playlist for a cool demo, then the 1st 4 videos (note: the video quality improves in later videos), then 10 and 11, then RayMarching starts in 22-24 and 29. (Many other videos in that channel are great for shader programming techniques, too.)