How do I get ONLY the music from a video downloaded off aTube Catcher?

I downloaded aTube Catcher because my friends can get music off
youtube  hear it on their Ipod, i try to end up ONLY with the music
but i get the music as a video. How can i change that or is it even
possible? I tried asking my friends how they do it  they say it just
happens so idk :l HELP!