This is a simple emergency stove that will boil water, cook a stew and provide a small amount of heat. You'll need an empty, clean paint can or something of similar size, hammer and nails, and candles.
Find a board or other solid piece that just fits inside. The idea is to keep the can from bending or collapsing as you put several holes in it, one to two inches from the bottom, with a nail and hammer.
Turn it upside down, and put three to five nails through the bottom. These will hold candles upright.
Set the can upright again, and punch several more nailholes about an inch or so from the top, then remove the board.
Spear the candles on the nails at the bottom, and using a twisted or folded length of paper as a torch, light them all. When they're burning well, place a pot or bowl over the open top of the can. If the flames go out, punch more nail holes at the bottom; then if they still go out, punch more at the top.
Trial and error will get it right, so spend some time on it now instead of waiting until you really need it.
A variation of the candle stove is to place candles in a row or group on some nonflammable surface and make a reflector of foil behind them. This puts out an amazing amount of heat, but be very careful with open flames. You'll need to watch constantly with this method in case of accident. Keep water nearby.