What is Diode?

It has two parts anode and cathde, anode is positive side and cathode is negative side.
Diode is like a valve, it starts conducting when it is in forward biased and stops when it is in reverse biased
now what is forward and reverse biased

farward biased means when anode is at higher potential and cathode is at lover potential like +5V at anode and -ive5V ,0V or 1V   any value less then +5V, in reverse biased anode is at lower potentential and cathode. 
it has voltage drop of 0.7 volt.