Answer:
This is easy enough but understand that the current output is very weak and will normally only power a low-watt light bulb for a short time. What you'll need is two clean copper wires (about eight inches long), a lemon (room temperature) or a potato (warmed but not cooked), a small low-watt light bulb, and two highly conductive and fairly stiff rods.
You just hook the wires to the light and to the conductive rods and incert the rods into the ends of the lemon or potato. Sometimes it even works better if you complete the circuit for a few seconds by just touching the wires together before you hook them up to the light. ( it just starts the chemicals inside so that you get a stronger output of electricity)