We have to start somewhere, so it might as well be here:
https://en.wikipedia.org/wiki/Electric_power
Real power (Watts)
Apparent power (VA)
Reactive power (VAR)
What this really means is the utility gets very upset at industrial customers that have very bad power factors. The bad power factors are usually caused by inductances from large motors.
So, why do they get upset? Because their transmission lines overheat because the currents are much higher than they would be for a purely resistive load. You really want the reactive power to be zero. You want all the power produced to be turned into energy and NOT returned to the source as essentially a circulating current.
PF =1 means that the cos(θ) = 0 for sinusoidal voltages and sinusoidal currents. It means that there is no phase difference between the voltage and currents.
You have to understand DC power first in terms that P= V*I and that a positive sign is power DISSIPATED. You also have to know when the sign is understood. e.g. a 16 MW power plant is really a -16 MW power plant and the homes dissipate the power. i.e. 16 mW = homes * power per home
Then you step up a bit and learn that if a load is resistive and the voltage is AC, the same P=V*I relationship holds and that the RMS value of the AC is the equivalent DC voltage to the same resistive load.
Then you move to voltages and currents are both sinusoidal and now P = V * I cos (θ)
And hopefully when you add a complex load like a VFD, a PC switchmode power supply, an electronic ballast, or even a non-electronic ballast the current waveforms are anything but sinusoidal. The simple relationships don't apply any more and it's likely that the devices will employ some sort of power factor correction. Power factor correction basically means the current drawn from the mains needs to be an average current.
See here:
https://www.electro-tech-online.com/custompdfs/2013/04/pfc_switchmode_powersupplies.pdf