Echo

echo is a command to write something. By default this goes to stdout which by default goes to the console. Here is an example:

tweedleburg:~ # echo "hello world"
hello world

you can also output variables:

tweedleburg:~ # export name="Linus"
tweedleburg:~ # echo $name
Linus

for more info on this, see shell programming. As with every program that outputs text, you can redirect the output to a file like this:

tweedleburg:~ # echo "hello world" > file
tweedleburg:~ # cat file
hello world