If I remember correctly: You simply play Rock-Paper-Scissors (one win = 1 point of damage). In addition the Hero's Rock would beat the Monster's Scissor for one additional Damage (2 in total) - so the system is geared slightly in favor of the Hero.
I found them at a local gift store selling each at SGD1. I bought myself a set but I'm not sure if they still carry them as they rotate their offerings fairly frequently.
These are rather cute, but you can always get the Koplow 12d dice for about $5.00 too. Similar to these (Chinese) are available on eBay, probably will be kinda cheap.
