There is a large amount of detailed information available about the X server, the clients that connect to it, and the assorted desktop environments and window managers.
C.7.1. Installed Documentation
/usr/share/X11/doc/ — contains detailed documentation on the X Window System architecture, as well as how to get additional information about the Xorg project as a new user.
/usr/share/doc/gdm-<version-number>/README — contains information on how display managers control user authentication.
man xorg.conf — Contains information about the
xorg.conf configuration files, including the meaning and syntax for the different sections within the files.
man Xorg — Describes the
Xorg display server.