1. Get inspired, get motivated. Shaders like these are breathtaking (and well-commented): https://www.shadertoy.com/view/l3cfW4
2. Watch "Learn to paint with mathematics" to see a simple shader being built gradually: https://www.youtube.com/watch?v=0ifChJ0nJfM
3. Work through https://thebookofshaders.com/.
He is essentially the god of shaders effects like this. He is the one who made Shadertoy, the non code-golfed version of the cloud effect, and the second video you linked, among many other things.
1. Get inspired, get motivated. Shaders like these are breathtaking (and well-commented): https://www.shadertoy.com/view/l3cfW4
2. Watch "Learn to paint with mathematics" to see a simple shader being built gradually: https://www.youtube.com/watch?v=0ifChJ0nJfM
3. Work through https://thebookofshaders.com/.