In laymens terms voltage is the force that moves the electricty, silmilar too pressure with liquid. Amperage is comparle to flow in liquid. Wire size is similar too the diameter of the pipe. Increase voltage( pressure) and you can decreas wire size( decrease pipe size in liquid) and acheive the same actual amout of power ( or flow rate). Take Amps and Voltage and you can determine actual watts of power being used. Wattage does not care about voltage and amperage, 100watts of power is a 100watts of power regardless of voltage. As in pipe with liquid you have pressure drop over long runs just as you have voltage drop over long runs of wire. With wire the higher the voltage the less detremental the voltage drop is over long runs as in why you always run a higher vlotage run and then use a step down transformer close too the service.