In Telecommunication industry and signal processing Modulation is used to carry information with the help of carrier signal wave. Common example is FM (Frequency Modulation) which is mostly used for broadcasting mus and speeches on radio. So in modulation analogue information is convert digital
and then this information is transmitted and then when this information received at the receiver it's demodulated and in this way information is transmitted with an efficient use of bandwith. Now in Demodulation the information is restored by reversing the mechanism which we used in modulation. Computer modem is used for modulation and demodulation. Basic idea is that computer generates a sequence of 1's and 0's from the information which is to be modulated because computer just understand binary languages so this information is modulated and converted into light waves and then transmitted over optic fibers and when its reaches destination light waves are demodulated bu modem and information is passed through destination.