It's an input, not an output. For example, as I don't have a USB BT dongle, I have a 2.5mm lead cable that goes out from my laptop headphone port into the AUX port.
Then, you press AUX on the speaker, and voilà sound comes out... without BT though... can't believe I need to buy a BT dongle to have BT work on this laptop... shudders.