How it works
A PNP transistor is the complementary counterpart to the NPN transistor. While an NPN requires a positive voltage at the base to turn on and conduct current from Collector to Emitter, a PNP requires a negative voltage (relative to the emitter) at its base to turn on, conducting current from Emitter to Collector.
PNP transistors are classically used as "high-side" switches. In this configuration, the Emitter is tied directly to the positive power rail, the Collector connects to the load (which goes to ground), and the Base is pulled LOW to turn the transistor on and power the load.
Because they rely on "holes" rather than electrons as their majority charge carriers, PNP transistors are inherently slightly slower and less efficient than their NPN counterparts, though this rarely matters in basic hobbyist circuits.