I don't really have a problem, I was just wondering where I could find some documentation about what exactly X server, Xorg, LightDM and stuff like that does.. I always stumble upon those terms, I know they have something to do regarding the graphics, but I'd like to know more.
X-Windows is a Unix/Linux Client-Server system. Although usually on the same computer, the Client and Server can be on different computers, unlike Microsoft Windows.
X11 is a network protocol. It encodes things such as graphic primitives, images, pointer motion, and key presses.
X clients are graphical applications like Firefox.
Xorg is an X server. It implements X11 and provides an interface to keyboards, mice, and video cards.
Gnome, KDE, LXDE, and Xfce are desktop environments. They provide libraries and specifications that applications use
When running X-Windows, instead of a console login, the Display Manager i.e. Lightdm starts up. The DM starts the X-server and asks for login credentials and then launches the user's desktop environment.
Hope that helps.
For background information on applications running on Ubuntu I always find the following resources useful:
For deeper insights or other views on applications that run in different distributions we can also find a lot here:
This list is incomplete, I know.
This architectural overview is a bit outdated, but still mostly applies: