To make it convenient for understanding, we use some logical value, say,
                        LOW (L)   -   will represent    0V and
                        HIGH (H)   -   will represent    5V

Computer is used to solve mainly numerical problems. Again it is not convenient to work with symbolic representation. For that purpose we move to numeric representation. In this convention, we use 0 to represent LOW and 1 to represent HIGH.

                                              0     means    LOW
                                              1     means    HIGH

To know about the working principle of computer, we use two numeric symbols only namely 0 and 1. All the functionalities of computer can be captured with 0 and 1 and its theoretical background corresponds to two valued boolean algebra.

With the symbol 0 and 1, we have a mathematical system, which is knows as binary number system. Basically binary number system is used to represent the information and manipulation of information in computer. This information is basically strings of 0s and 1s.

The smallest unit of information that is represented in computer is known as Bit ( Binary Digit ), which is either 0 or 1. Four bits together is known as Nibble, and Eight bits together is known as Byte.