We like to dip candles rather than pour them into a mold. Dipped candles are fun and easy. Young children will need supervision. Break pieces off the block or sheet of wax, and place them into the coffee can. This can be hard work, depending on the shape of the block.
Smaller chunks melt faster, but the size is only important for fitting the wax into the can.
The more wax you put in the can, the deeper the melted wax will be, and the longer your candles will be. Place the can with the wax into the pot. The water should come up about halfway to the top of the outside of the coffee can. Now you have a double-boiler for wax. Heat the water to a boil, watching occasionally for melting wax.