Fundamentals of Shading Course and Principled BSDF

All I know is that the principled shader is more physically accurate.

Welcome Richard, great question. We do have lessons on PBR shading and the Principled shader here: https://cgcookie.com/lesson/pbr-introduction

While it definitely makes basic shading much easier, it doesn’t do everything, so you’ll still need to know how other Cycles nodes work and how to mix them, which is exactly what the Fundamentals course covers. I would recommend finishing the fundamentals course, then watching the non-Principled PBR videos, and then the Principled video last so that you’ll have a good understanding of what’s going on behind the scenes and can make any material you can think of. 

One last question, when you’ve used nodes to apply certain material effects such as Fresnel, etc – do these qualities get carried over when exporting them to other engines?

Unfortunately not, shaders and properties of one render engine won’t carry over to a different engine since all of them use different approximations and variables to come to the end result.

This is a nice tutorial to get the bigger picture about computer graphics. It helps youto see the bigger picture what goes on in which stage of the rendering pipeline:
– https://www.ntu.edu.sg/home/ehchua/programming/opengl/CG_BasicsTheory.html