lets you write shorter aliases for your commands.

Say you always use the -almost-all and -color=auto options to ls. You
quickly get tired of typing ls -almost-all -color=auto. So you make an
alias:

alias myls='ls -almost-all -color=auto'
Now you can type myls instead of the full command. To see what myls really
is, run the command type myls. To see a list of aliases you've defined,
simply type alias on a line by itself.

Controlling Input and Output

Throughout your experiences with Linux, you will most likely find that
manipulating application input and output can be a very powerful thing to
do. This section describes some of the things that controlling input and
output can do for you.

stdin, stdout, Pipelines, and Redirection

Every process has at least three connections to the outside world. The
standard input is one source of the process's data; the standard output is
one place the process sends data; and the standard error is a place the
process can send error messages. (These are often abbreviated stdin,
stdout, and stderr.)

The words ``source'' and ``place'' are intentionally vague. These standard
input and output locations can be changed by the user; they could be the
screen, the keyboard, a file, even a network connection. You can specify
which locations to use.