What are the functions of emitter, base and collector in a transistor?

Which type of transistor is shown in the given figure? In this there are two $p-n$ junctions (i) between the emitter and the base and (ii) between the base and the collector. Which one of these is forward-biased and which is reverse-biased?

Would you prefer to use a transistor amplifier in common-base configuration or in common-emitter configuration? Why?

In a transistor, whether common-base or common- emitter, we obtain power gain. Does it mean that transistor generates power?