Purpose of shaders?

Hello everyone, I know that there is shaders scripting language that has something to do with graphics, but I never understood almost anything about shaders. How much and what difference can be made with shaders, what do shaders change and do what can be improved with them? My question is: What can be done with shaders that can’t be done with simple materials that have certain values for metallic and smoothness or image effects??
Thanks in advance.

A shader is the underlying code of the materials. So from your point of you shaders and material are practically the same thing.

A shader is a piece of code a programmer has written. A material is what an artist creates by setting different values for that shader.

A shader tells the engine how to render a certain material. That’s basically it.