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Diode is a two terminal device that allows current to flow in only one direction.
It contains an anode and a cathode.
This current that flow in the direction from anode to cathode.
The flow of charges forms current which makes it to work.

A diode is the simplest sort of a semiconductor's a two end electronic component . it has low resistance of the flow of current in one end and high resistance in the other. 
 a semiconductor diode is the most common now-a-days..made up of crystalline
piece of semiconducting material and having two ends/ terminals on the front and the back.
 its applications are---> 
1)in radio demodulation--> The first use for the diode was the demodulation of amplitude modulated (AM) radio broadcasts
2)power converters.
3)over-voltage protection
4)temperature measurements and a lot more.