[HELP] Information on shading models / features, ES2, SM5 ect.

I am an env. artist working with UE4 materials for the first real time and I’m building a multilayered vertex blended material. I got a ES2 warning for going over 8 texture samples. Is there a place for more information on shader models? I found this (ERHIFeatureLevel::Type | Unreal Engine Documentation) page by searching but can’t find any coherent info.

Thank so much.