These are done by using your computer printer, white tissue paper and a craft heat gun.
Figure out the size of the area of the candle you want the design to cover
Using a drawing program on your computer (I use MS Publisher), design what you want to appear on the candle.
You can put photos, words, clipart, anything on them
Tape white tissue paper about 1/4 inch in on a piece of cardstock and run it through your printer so the design ends up printed on the tissue paper
Trim your design of excess tissue paper
Place it against a candle, and heat with the craft gun
As the wax melts, it saturates the tissue paper, making it "invisible" and leaving only the design on the candle.
Try it with a simple design and see how easy it is