Transistor are two types, they are pnp and npn the case of a pnp transistor there are3 regions.emitter,base ,and emitter is p type semiconductor ,base is n type and collector is p type emitter is moderately dopped,base slightly dopped, and collector is heavily dopped ,dopping means adding impurities to increase electrical two junctions are there,pn junction and np junction.transistor is used for amplification ie for strengthening the input signals.when connected to the circuit,emitter-base is reversebiased and base-collector is forward biased