Don't worry about finding all of this being "a bit confusing"! I've been at it for over a year, and still get lost!
I haven't even bothered to really look into sound yet... manipulating the pictures is already not an easy task! As for sound, I could be wrong, but don't really think you can edit it in Flash. You could always put a stop before lyrics jump in, but as far as I know and have experienced up until now, that would be about it.
I'm an editor by trade, so I have a lot of applications that can edit waves (Premiere, Goldwave...), and I have been using those for the small sound work I have done. BTW, don't know if you can edit MP3s... you might have to reconvert them to waves! But I could be wrong... I'm so old!
Take care! And don't hesitate if you have other questions...
Somebody else, if not me again, may have an aswer for you!
;-)
"If nothing else, I can always serve as a bad example!”