how is the BSDF function used in the kajiya rendering équations ? We know that path tracing proivde an analytical solution and we saw the BSDF function at first time in the path tracing algorithm. After that, is there a way to use mutliple BSDF function in a full rendering process ? If you have some links to any books or website, please share it !

Do you mean a material describing the surface properties ?

And Welcome ?

Yes, this is what I mean. Sorry if the question is a little bit not clear, I have a team and I'm an engine programmer, and currently not really a talented graphics programmer.

No problem. Some links i know of that describe the whole thing from the practical side:

The series "In One Weekend"

Another intro tutorial

Te book Physically Based Rendering. I think there is an open source version as well. I have only had a short glimpse. It is not a light weight ...

There are couple-few nice SIGGRAPH courses covered the topic in some sort of degrees, for example:

Physically Based Shading at Disney

Extending the Disney BRDF to a BSDF with Integrated Subsurface Scattering

Practical Multilayered Materials in Call of Duty: Infinite Warfare