What is colour code of resistors , Please explain ?

Colours to denote value.

In four band colour coding, the first band indicates the first digit, the second band : the second digit and the third band : the number of zeroes.

The values are as given below:

Black : 0, Brown : 1, Red : 2, Orange : 3, Yellow : 4, Blue : 5, Green : 6, Violet : 7, Grey : 8, White : 9.