I recommend checking out the Blender Manual linked here. You will get an overview of what each node will do with some examples. Well worthwhile if you want to seriously grasp the basics of cycle. There are plenty of tutorials posted on YouTube if you care to spend time watching the videos and taking notes. There are also plenty of images with shader node arrangements scattered throughout the internet and readily available if you do a Google search.

There is nothing that can be done about the absence of critical nodes, the coding in Poser does not lend itself to such features so you may need to be creative and construct an alternate compound node to fit your needs. Forget any nodes with curves, the feature does not exist at all in Poser and introducing them will destroy backward compatibility with P11. As for the latest P12 PrincipledBSDF and PrincipledHair nodes, they will prove useful. I've used the PrincipledBSDF node successfully for improved SSS for skin; the PrincipledHair needs to be worked with to achieve the right balance for strand-based hair, there hasn't been enough testing yet to find that sweetspot.