Using Ubuntu and AskUbuntu, I see all these key words:
- Linux Kernel (header)
- Gnome,
- Grub, Grub 2,
- Xorg,
- Unity,
- Compiz,
- Metacity,
- ...
Could I get a view about those components (and probably other main components) to understand how they are linked together (with a small definition of their purpose)?
Here's an overview of the Ubuntu architecture.
Beyond that just looking them up on Wikipedia or Google would be a good way to understand more and to see which ones relate.