Q. What are the basic operations of  MOSFET?

The gate to source voltage is set to zero volts by the direct connection from one terminal to the other,and a voltage Vds is applied the drain to source terminals.The result is the attraction for the positive potential on at the drain by the free electrons if the n-channel and a current similar to that established through the channel of the JFET.In fact the resulting current with Vgs=0V continues to be labeled Idss.

V_gs has been set  at a negative voltage such as -1V.The negative potential at the gate will tend to pressure electron towards the p-type substrate and attract holes from p-type substrate .Depending on the negative bias established by V_gs ,a level of recombination between electrons and holes will occur that will reduce the number of free electron in the n channel available for conduction .The more negative the bias the higher rate of recombination .The resulting value of drain current is therefore reduced with increasing negative bias for V_gs.