Here's how it works. That means you count five on the first hand and add two from the second, to make seven. After you run out of fingers, go for the toes. That means you add all ten fingers plus three toes. The counting system we use has a base of ten.
Larger numbers are simply multiples of ten.
For example, ten tens make one hundred. We're so used to our base ten system that it may seem like the only possibility. But the Greenlandic number system has a base of twenty, and others have a base of five. Of all the number systems ever invented, five, ten, and twenty are the most common bases. It's no coincidence that these bases match the number of fingers on one hand, or two hands, or all of our fingers and toes.