Imagine you have 10 fingers. That's why we use the number 10 for counting things. Each finger represents one number, like 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. When we run out of fingers to represent a number, we add another set of 10 fingers and start counting all over again. That's how we can count bigger numbers like 10, 11, 12, and so on. This system of counting is called the decimal system.