I just bought a pair

Question

I just bought a pair of "istar" USB speakers which came with no instructions. I have put the usb into a port at the back of the computer and plugged the little green (sorry not real tech savvy lol!) plug into it's socket too. The speakers turn on, but how do I now get the sound to come out of the speakers. I have been trying to test it listening to youtube and nothing comes out - it's still coming out of my computer and the sound in my computer is quite distorted (which is why I got speakers). Can anyone tell me what changes I need to tell the computer in order for the speakers to function? Cheers, MUMOF4