One thing Ed's article didn't mention (although no doubt it is in the other links he posted) is the relationships between volts, amps and watts.

power = volts x amps (and we measure power in watts so watts=volts x amps).

Thinking of the water analogy again imagine a big old wooden waterwheel (the sort that might have powered a sawmill in times gone by). Now imagine hitting that waterwheel with a supersoaker water pistol - very high pressure, but low flow (so high voltage, low current) - the wheel would hardly move. Then imagine the gently babbling creek feeding the water wheel and it turning slowly (so low voltage, high current). Finally imagine a fire hose hitting the wheel and it spinning quite quickly (so, high voltage, high current).