1. Insert one steel screw and one copper penny into each lemon. The more lemons the better as well as the further you stick the screw and penny into each lemon the better. Both aspects will make for better voltage and amperage.
2. Connect the alligator clips in series, going from the screw in one lemon to the penny in another or in parallel, going from screw in one lemon to screw in another and penny to penny.
3. It should power the led as long as you have everything set up correctly.
Tips if you are having trouble getting it to work
1. Which alligator clip you have connected to which end of the led matters, so try switching around the ends to which the alligator clips are connected.
2. Add in more lemons. The more lemons the more voltage and amperage.
3. Push in the screws and pennies for greater voltage and amperage.
4. Some led's are bad. So try different led's.
5. Try different fruits. Different fruits will give you different voltages and amperages.