Thanks 
I think you just gave me a dictionary when I hoped for guidance about how to read ! - have you a gentler introduction on the topic of what these things are and how they work rather than what they do :-)?
There is lots of stuff in your links but there’s nothing in overview that says what the architecture of discourse is - I’m less concerned with what capabilities are provided in the plugins etc at the moment - I’m still trying to work out what they actually are