We use decimal system of numeration in our daily lives but computers don't. Computers use binary mathematical notation which has digits 1 and 0. The explanation why it is implemented and widely used because its really easy to store 2 states of knowledge instead of 10.
Binary mathematical notation is employed to store information in computer. Binary numbers are more accurate and readable mathematical notation. Performing calculations is perfectly easy with these numbers. Binary numbers system has 2 logic systems. They are positive logic system and negative logic system.
1)Positive logic system: 1 is represented as true or with +5volts.0 is represented as false or with volts.
2)Negative logic system: 1 is represented as false or with 0volts.0 is represented as true or with +5 volts.
Converting binary number to decimal:
Decimal to binary conversion
Fractional decimal number to binary conversion