\newcommand{cmd}[args]{def} \renewcommand{cmd}[args]{def}
These commands define (or redefine) a command.
cmd
\
. For \newcommand
it
must not be already defined and must not begin with \end
; for
\renewcommand
it must already be defined.
args
def
cmd
; a
parameter of the form #n
in cmd
is replaced by the text of
the nth argument when this substitution takes place.