oh boyee...
Ohms symbol Ω is the measurement of resistance in a conductor to the flow of electricity (similar to a kink or drag of water in a water hose)
Voltage symbol V or E depending on whatever formula you are looking at is the measurement of the PUSH the electricity has on it in that same conductor (similar to the water pressure of water in the hose)
Current symbol I or amps is the measurement of the actual amount of electrons in that conductor (similar to the amount of water flowing thru said water hose)
The resistance of the coil in conjunction with the voltage of the device determines how much "power" or watts is available to turn electrical energy into heat energy, the efficiency of the heat energy to transfer to a liquid medium in order to cause to boil (vaporize) is dependent upon many things
High watts = more heat energy however too much heat energy = converting the oils of the e-juice into carbon (thus the nasty licking a charcoal briquette) taste
Low watts= less heat energy which means it will take longer to heat the e-juice to make steam (vaporization)
In order to mathematically calculate power you use a formula called OHMS LAW E/I X R,
Voltage divided by
Current times
Resistance (rememeber in highschool when you said "when will I ever use this algebra crap" well...howdy doody)
Since you know the voltage of your rig and the resistance of the coil you can calculate current flow, current flow can then be converted to watts (aka power)
Raise the voltage or lower the resistance is how you tweak your "power" of your rig (thus the VV (variable voltage) rigs)
Using the math is just a starting point (it also gives you a operational parameters that your rig/coils should be able to safely handle)...ultimately you will learn how to tweak your rig or coils in order to get the best vape...just remember you CAN overdrive your rig, resulting in burnt out coils, heated/shorted explody batterys...