"For many computer users, it sounds like a nightmare: being
forced to enter cryptic commands into the computer using the
keyboard. Yet it need not be such a horror show. While operating
systems like Windows XP and Mac OS and many Linux versions allow
the user to completely control the computer using the mouse, it can
sometimes be helpful to enter commands in text form. Linux offers a
powerful tool for this, known as the 'console' or 'shell.'
"A command consists of a series of letters or symbols capped off
by the return key. The command is then evaluated by a command
interpreter, known as the 'shell.' There are various shells..."