Double boiling is simply, using in-direct heat to melt or cook something. Using either a dedicated Double Boiler or a sauce pan and bowl, you can safely melt chocolate or almond bark or make custards and sauces.
Place water in the sauce pan, bring to a boil or simmer. Place a bowl with an opening slightly larger than the sauce pan inside the sauce pan. Place your contents in the bowl and let it slowly melt. Most of the time, you’ll want to keep stirring.