It's just like any other data, except there are a couple of special considerations for "streaming"...
Are you transmitting, receiving, or both? What are you communicating with, and does that other device use a particular serial protocol? Do you need to store the audio? What kind of "processing" is the Arduino doing?
The "special considerations" are that audio needs to be buffered because it needs to flow continuously and smoothy (or apparently smoothly-continuously ) when the processor is off doing other things (like proccessing the audio data, or switching between transmitting/receiving, etc.) Also, audio takes-up quite a bit of memory, and needs high speed transmission (depending on how much audio you are storing and what quality you need).