Hi there,
I made a flash movie but it takes a long time to load, so I realize I have to make a loading screen.
Well, I made one, but I don't know how to get it into my movie.
What do I have to do?

if your main movie is main.swf, then in your movie with the loading bar you can
use:

_root.createEmptyMovieClip("targetMC",1);
_root.targetMC._alpha=0;
_root.targetMC.loadMovie("main.swf");
preloadI=setInterval(preloadF,100);
function preloadF(){
loaded=_root.targetMC.getBytesLoaded();
total=_root.targetMC.getBytesTotal();
// loadBar._xscale=100*loaded/total; or whatever you want here for your
loading bar.
if(loaded>=total&&loaded>0){
clearInterval(preloadI);
_root.targetMC._alpha=100;
}
}