Tableau documentation is generally not bad. However it is not the best source to understand the internal architecture of Tableau Server: I've been searching the forums with most of my questions regarding how the pieces fit together. And when it comes to the big picture, I really missed one "big picture" to visualize the core of the visualization BI server. As I couldn't find it, proceeded to create one, using this excellent old pic from Prazval Ks as a starting point.
It hopefully helps you when reading the official page about server processes -- it certainly did help me.