How does the transistor amplify? is it when the voltage from emitter flows through collector when the acquired voltage from base have reach?

 

Carefully read:-
http://www.allaboutcircuits.com/vol_3/chpt_4/5.html

Also:-
http://en.wikipedia.org/wiki/Common_emitter

 

Base current is multiplied by a factor called beta; i.e. Ic=(beta)Ib. You can multiply the current by a resistor value to get voltage.

 

thank you it helps me a lot