It's very basic and you've done it right by playing the sound already. copy & paste maybe?

I asume you're trying to pause the sound asset:
ISound(assets.myMusic).pause(true);
I hope I don't sound too condescending, but you'll have a hard time with Gaia if you don't know at least the very basics of actionscript. For example something like "pause(flag:true);" is syntactically wrong.
Hope it helps