It is pretty cool! But I can't use it anymore cause I don't have an apple product. It shoulshould work for ipod4. I know it works for iphone 4 and I believe they all use the same plug.
There is a place on the bottom, you plug the wall charger or usb to the computer in to charge it up. then u can take it anywhere and if your phone/ipod is running low on battery, plug in the external charger and it will charge your phone up...i think it was like 30-60% more, i dont remember exactly.