Can any one tell me how is quscient point in transistors are useful.and what are they

 

http://www.electronics-tutorials.ws/transistor/tran_2.html

 

what is quscient point?

 

There is no such thing as a quscient point. If you mean the quiescent point, this was defined in the link you were given by dcarson7

...It is necessary to set the initial value of Vce correctly to allow the output voltage to vary both up and down when amplifying AC input signals and this is called setting the operating point or Quiescent Point, Q-point for short...

The quiescent point is the DC condition under no-signal conditions, and about which the signal variations take place. In other contexts, the word "quiescent" means "resting" or "inactive".