OKay, lets break it down a bit.
Voltage is the quantity of stored energy. Think of this as a big water tank on a hill. You can adjust the voltage in a number of ways. One would be having a much bigger tank. Another would be to lift the tank up HIGHER in the air.
Ohms is the resistance in the system that will be using the energy stored up in the tank. Think of this as the size and length of all the pipes that will be used to move the water from point A to point B.
Watts is the total power or amount of water that's going to come out of a spicket at the bottom of the hill when you turn it on.
Amps are the current, or 'speed' that the water will flow through the system.
Power and Amperage are altered by either changing the resistance (size and amount of pipes) and/or changing the voltage (height and/or size of the water tank).
If you lower the resistance, the water flows faster, and you get more water coming out of the spiket.
If you raise the voltage, the pressure on the pipes goes up...pushing the water though faster.
So with all that in mind...you can enter you target wattage and resistance into the calculator and find out what the amperage and voltage will be. Or, you can enter the voltage and resistance and see what the wattage and amperage will turn out to be.
Resistance:
If you use bigger and/or shorter pipes...the resistance gets LOWER, and the water flows faster.
If you use smaller and/or longer pipes...the resistance gets HIGHER and the water flows slower.
You can also effect resistance by how LONG the pipes are. Longer pipes will have more resistance than shorter ones.
Note that wire size can be a little different from water pipes. The wire we use for making coils in vaping is an alloy, or mixture of conducting and insulating materials. Larger sized wire with more conductive and less insulating alloys will typically have less resistance (more conductive material for energy to flow through), while smaller sized wire with less conductive and more insulative properties may have higher resistance (less material for energy to flow through).
Why are amps (current) important?
This is potentially the most dangerous part of dealing with electricity. If power flows too fast, it can suck the energy out of the battery (water tank) too fast and cause it to reverse polarity (think of this kind of like a water tank being emptied too fast...it could cause it to implode).
As far as batteries go...they have a maximum current that their chemistry can safely dump energy. Trying to dump it too fast can cause too much heat, or as mentioned above, invert the polarity of the storage centers in the battery.
At the end of the spiket are your WATTS, or resulting POWER.
Safe amperages are determined by the battery's C rating. In general, it's good to keep the maximum amperage your atty build will draw to about half of what the battery is rated for or less, although some people push it beyond that. In short, if you mess with sub-ohm stuff...don't mess with any battery that isn't rated for 20 or more amps.
If you use a regulator like the Kick, or you don't plan to sub-ohm and your mod has a compression spring or you use fuses, and you know you're not going to push your battery beyond say...7amps...ever...you could opt for a higher capacity hybrid cell rated at 10 amps.
I hope this helps a little...if not, keep asking questions