"Can u explain how amplification is done"
@user3252171 - let me try to answer your question. However, at first I must direct your attention to the fact that in the answers given up to now you will find two different explanations for the collector current control mechanism.
Hence, we need the answer to the question: Is the collector current Ic controlled by Ib or by Vbe ? Only one answer is possible. And the answer is: Ic=f(Vbe).
The collector current is controlled by Vbe and NOT by Ib. Ib is a result of the applied base-emitter voltage but it is neither the cause of Vbe nor Ic. On the other hand, we have a - more or less - fixed ratio between Ic and Ib (called current gain B resp. beta), but this is a simple correlation and has nothing to do with a control mechanism (causation).
Don`t get confused - I know that these two different (contradictory) explanations can be found also in textbooks. The reason may be that during calculation of transistor-based circuits these physical properties are sometimes overlooked. It is, however, surprising that all people make use, of course, from a bias voltage Vbe (in the range 0.65...0.7 volts). Nevertheless, some of them still think that this voltage would have no controlling function. A severe misconception - because there are many effects, circuit properties and working principles which can only be explained based on voltage control.
Now - the correct knowledge of the BJT`s control principle is the key to understand how the transistor can amplify: There is a transfer characteristics which relates the transistors input (Vbe) to the transistors output (Ic):
The classical equation formulated by the great W. Shockley: Ic=Io*exp[(Vbe/Vt)-1]. Now - asking for the small-signal gain we need the SLOPE of this function which is called transconductance gm=d(Ic)/d(Vbe).
This parameter gm is the gain determining parameter because it says how much the collector current will change its value as a result of an input voltage change d(Vbe)=d(Vin). If we use Ohms law (and a collector resistance Rc) to transfer the output current change d(Ic) into an output voltage change d(Vout)=-d(Ic)*Rc we have an amplifying stage with the gain A=d(Vout)/d(Vin)=-[d(Ic)*Rc]/d(Vin)=-gmRc.
This simple formula gives the gain for a non-stabilized stage. Because of several reasons (stability against temperature variations, parts tolerances,..) we normally make use of emitter degeneration (negative feedback) in form of an emitter resistance RE. In this case, the gain is A=-gm*Rc/(1+gmRE).
(The minus sign results from the fact that the ground referenced collector voltage is Vc=Vout=Vcc-Ic*Rc and d(Vc)=d(Vout)=-d(Ic)*Rc because d(Vcc)=0. Hence, we have amplification with phase inversion.)