The USB's would be used if you wanted to put music on a thumb drive and play audio or you could connect your phone to the radio via a cable. Or both. You could add a cd player to the radio also using the aux input. Or just about anything else. Including your phone using your head phone output from your phone. This thing is very versatile. Though I cannot see using more that any 2 inputs at any time. I only use 1. And that is the Blue tooth connection. No wires. And play music from the web. I use Pandora and occasionally Sat radio.
