Summarize this article:

Fill a large pot with 1 to 2 inches (2.54 to 5.08 centimeters) of water. Place a heat-safe glass container inside the large pot. The top of the glass container should be above the water level. If you have a metal beaker used for candle-making, you can use this instead of the glass container.

Summary:
Assemble a double boiler or bain marie.