loading sounds with urlrequest, i dont understand.

[omniscient232]

in this piece of code:
PHP Code:
var mySoundReq:URLRequest= new URLRequest("samplesound.mp3");
var mySound:Sound = new Sound();
mySound.load(mySoundReq);

How does the urlrequest know where that .mp3 file is located, and how do i tell as3 where it is?

and another thing: when i put this on the web, how do i locate the file then?