The Power system works counting every your stats and result in power. The stats that will interfere in your power are: Every Skills, Ninjutsu, Level, Health, Chakra, Jutsus learned, Bijuus sealed in yourself and bijuus sealed in statue. They will result in your total power. To check your power you need open the page stats in game.

You can also check the stats of another players. Its a good idea before starts a battle!

The power is not only to check who is more stronger, this also return a value of health when you take a damage. (More power, more heal.)