1. The document discusses different number systems like binary, octal, decimal, and hexadecimal that are used to represent numbers in a computer.
2. In binary number system, only two digits 0 and 1 are used. Each place value has a weight like 20, 21, 22 etc. This allows numbers to be represented using a combination of 0s and 1s.
3. Common operations like addition and subtraction can be performed on numbers in different number systems as well. Decimal numbers are easily converted to other number systems and vice versa.