very green with Linux, need USB sound help on BBB

I am very new to Linux, trying to do some learning, have gotten a BBB to play around with. I have the newest BBB with Debian and need help with some basics to start with. I am getting a handle on the structure of Linux and am not too uncomfortable with a command line interface. I am trying to reset my BBB default audio device from the HDMI to a device on the USB port without success, is anyone available to give me some tips? Thanks, Jim