Variable Voltage/Wattage can also be termed as Constant Voltage/Wattage.
This can be compared to your car thusly:
Variable/Constant Voltage is like holding your car's gas pedal (the voltage) in one spot. The car will increase and decrease speed (your vaping experience) as it goes up and down hills (the resistance of the atomizer). Your vaping experience will vary as does the speed of the car.
Varible/Constant Wattage is like engaging the speed control on the car. The car will maintain a constant speed (your vaping experence) while the gas pedal (the voltage) moves up and down in response to the hills (the resistance of the atomizer) the car goes up and down. Although this will use a bit more gas (watthours) and your battery may not last quite as long, your overall speed (vaping experience) will be quite constant.
Now, if I've not totally confused you, would someone please tell me what I just said???