Need a speaker for Computer

Hi,


I know nothing about electronics and that electricity can kill.


I would like to build a small speaker for my computer that uses an optical input cable from my computer peripheral. I would like to know if there is a kit out there and I would like to know if if can be powered by a USB port.


I just want one speaker and it is something I would like to do whilst there is very little to do and to satisfy my curiosity.


Thank you for your help


K