Switching between virtual consoles and the graphical environment

A typical Linux system will run six virtual consoles and one graphical console

Server systems often have only virtual consoles
Desktops and workstations typically have both

Switch among virtual consoles by typing: Ctrl-Alt-F[1-6]

Access the graphical console by typing Ctrl- Alt-F7

Operating system structure

A shell is a piece of software that provides an interface for users to an operating system which provides access to the services of a kernel.

the kernel is the central component of most computer operating systems; it is a bridge between applications and the actual data processing done at the hardware level.