Quantities can be grouped in different ways.
A number system is a way of grouping a value. Instead of this: We can group the dots like this: 2 groups of 10, plus 8, or 28. If they were eggs we might group them like this: 2 groups of 12, or 2 dozen, plus 4. In the binary (base 2) number system we would group them like this: 1 group of 16, 1 group of 8, and 1 group of 4. (There are no groups of 2 or 1) The number of dots in each picture is the same. They are just grouped differently. The number system we use every day, the decimal number system, is based on 10.
Number systems: grouping