It may sound confusing, but I believe it is easier to show than to tell. [He holds out one finger on each hand.] For example, if I were to "tag" my other hand, I would have to add the two numbers together and show that number on the hand I tagged.
[Demonstrates by lightly tapping one hand with the other and then extending another finger so that he would have two on that hand.] And if I were to tag someone with my hand that has two fingers then they would have three points and have to show three fingers. Unless the number of points they get on their hand comes exactly to five--not over--then their hand is not "dead."
Does that make sense? It's basically a game of strategy. It is more challenging if there are more people to play it, but you can play with two.