Grind the top of the other led flat.
If you are going to use 3 NiCd rehargeable batteries, you wont need any other components. With 3 alkaline batteries you will need a small resistor (somewhere between 5-10 ohms, I think).
Observe correct polarity - longer connecting wire of a led is the Plus-connector.
Three-way switch is also needed. Third position is for Total Darkness
(not depicted below , use your imagination :-).
(c) Timo Noko 1999