Blender/ Udemy Course
I worked through a few more lessons. These covered using nodes to control how the lighting effets are applied. There are surface and volume nodes. Blender node are represented by boxes with line that attache to one another like a flow chart. You could have a node that is a image or texture that feeds into a mixer that also has a node that feeds it another shader that then feeds yet another.
I added some subsurface scattering and layer weights to the head.
One lessons recommended playing with the different nodes to get an idea how they interact.
I continued reading Cartooning the Art and Business by Mort Gerberg