How to current flow in a transistor?

based on the type of transistor, the curent flows, if NPN transistor or PNP

as at the NPN transistor, the current flow from the collector to emitter, when the base signal is active and the oppositte for PNP Transistor

if you look at the transistor symbol, you can see an arrow, which refers to the current flow direction in each type of transistor

Current flows in a transistor by applying a voltage in its base terminal.