I'm not sure why you want shaders if you are just trying to move on from very basic games like the one you included in your post. You should probably be focusing on learning things like animation, movement techniques(wall grabs, sliding, double jumping, crawling, etc), attacks/weapons, UI/UX, items, text interfaces, cameras, mapping, enemies, I mean I could go on there's a myriad of things that you could probably benefit from learning before shaders.
If you insist on learning them I would dive into the wiki portion on shaders:
https://love2d.org/wiki/Shader, it's not ideal I know but that's how I learned most of what I know about love.physics(which still isn't even close to everything). Just dig in, experiment, and be persistent.
Hopefully someone can help you but you might as well try to figure it out on your own in the meantime, good luck!