Read how base, emitter and collectors are doped and what will be the size of each region. How much minimum voltage is needed to forward bias eb, cb junctions.
Make an experiment and find out what voltage you need to forward bias the eb junction of NPN transistor.
Make another experiment snd find out minimum voltage you need to forward bias the cb junction (c is N type and b is P type in NPN). So, connect collector to GND and base to +ve voltage.
Use a multimeter to check the forward resistance of eb and cb junctions.