Answer:
Number systems is a technique that represents and work with numbers. Every value saved or got into or from a computer memory is called number system.
Binary number system, hexadecimal number system, octal number system, and the most common decimal number system are examples of Numbers System.
The rules is important since all the numbers can be structured in a way to be enumerated and organized correctly. If we didn't use rules for number system we wouldn't make any progress in the society.