1. Light the candle
2. Surround it with 3 large mason jars or other non-flammable items that will act as the stand to hold the pots in place
3. Set the pots upside down above the candle and...
It takes a few minutes before it feels warm to the touch because the inner pots heated before the outer pot will retain heat.
Keep in mind that the last thing you need in a blackout is a fire. Make sure all materials are on a non-flammable surface. One idea is to put all of the pieces inside a large cooking pot.
One candle will heat up pretty well. If you can get a glass jar candle that has two or three wicks even better!