simple. just grag it into an empty layer

But all my music files are mp3 and they dont work D:

Oh and also I'm animating my battle against you.

i know, me too, i'm finishing my bg

you're using pivot or flash?
if pivot here http://www.youtube.com/watch?v=pRyi9rStxf8
http://www.droidz.org/stickmain/ <<< here is some nice stick ficgures and sounds and what not. pivot packs.

Flash D:

My song turned out squeaky! What is wrong?!

Mp3 doesnt work, use Wav.

http://www.youtube.com/watch?v=Wz90XNeeKy0 <<< flash sound importing

http://www.youtube.com/watch?v=DOPQeinpA-I << mp3 to WAV conversion

I did use wav [I used SSBB Main theme song] but it was faster and sqeaky sounded.

Purely as an exposition of your problem: mp3's will not work if they are too high quality. Following this through to its conclusion, strictly as an intellectual exercise, if one could find some lower quality source for one's mp3 then one would not come across such a problem. But I certainly wouldn't know anything about where to find low quality mp3's, and no one else here could help either.

Or adjust the audio quality in Flash. File>Publish Settings>Flash:

In the export settings, change the stream and event output to somewhere around 48 kbps or 128 kbps
EDIT
the above post describes it all

Okay I'll try it out.