Callin a function

Hey GUys,

Been practicing actionscript etc.
Came across this game tutorial and saw the following code:

function moveStuff() {
if (Key.isDown(Key.LEFT)) {
this._x -= 5;

box_mc.onEnterFrame = moveStuff;

For some reason i thought, when you call a function you have to end it with curly brackets. ie. moveStuff();

How come this isnt the case??