Problem of Preloader and Transition for Dynamic Files!

the tutorial from Flash MX: “Preloader and Transition for Dynamic Files”

i dont understand what is the meaning of " _root.section" whats is the mean of the " section"

and i put this script:

onClipEvent (enterFrame) {
if (!loaded && this._url != _root._url) {
if (this.getBytesLoaded() == this.getBytesTotal()) {
loaded = true;
_root.transition.gotoAndPlay(“opening”);
}
}
}

into the “content”, but the loading it doesnt work, is it any thing wrong??
and my “content” is put it second scene.

can any one help me?
thanks