What is the process of starting a Lubuntu session?

Hi all!

I want to understand the whole process of starting a graphical user session in Lubuntu 19.10.
I mean, what are the files involved? and in which order they are executed?
I suppose there is a main file that connects them all, like an init script for X. Maybe I’m using wrong terms for concepts, so please bear with me.

I looked into the Manual, but it is about more general usage, and no technicalities.

X is usually started on many if not most distros these days by having systemd start the display manager (sddm in our case). Hopefully that helps get you started…