A double boiler is a method to melt chocolate and other similar ingredients in a way that ensures it does not burn. Use a small saucepan and put a few inches of water into the bottom. Get a metal or glass bowl that is about 1½ times bigger than the saucepan, so that you can place it into the saucepan but the bowl does not touch the bottom. You will boil the water in the bottom saucepan while putting your chocolate (or whatever you are melting) into the bowl on top.