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.