Far to be an expert.
Physically based rendering (
PBR) is a
computer graphics approach that seeks to
render images in a way that models the
flow of light in the real world. Many PBR pipelines aim to achieve
photorealism. Feasible and quick
approximations of the
bidirectional reflectance distribution function and
rendering equation are of mathematical importance in this field.
Photogrammetry may be used to help discover and encode accurate optical properties of materials.
Shaders may be used to implement PBR principles.
Just to see something and understand how they works.
freepbr.com
Personally I've also used this free software to make some of them.
boundingboxsoftware.com
Here there's also a guide:
PM:
I hope I haven't upset anyone with my simple explanation. There are certainly passionate professionals here who will surely be delighted to give you further explanations about this.