To answer the question without going off of the rails more than I/we have, Watts is a calculated value, based on the speakers impedance and the voltage/current from whatever it's connected to, whether it's an amplifier, a battery, an outlet, lightning bolt, etc.

A speaker doesn't draw Watts, nor is it 'fed' Watts- the amplifier's output voltage can be present without a load, but no current is 'flowing' until a circuit is completed, with or without anything more than a wire. Current is the quantity of electricity carried in one second by a current of one Amperes- (one Ampere being defined as 1 Coulomb per second), Coulomb being the units for a specific quantity of electrons.

If you want to think about this in terms of water, Voltage is like water pressure, Current is like water flow and resistance is just that- resistance to current, which can be constant (bend a hose to cause a specific rate or bend it and vary the effect). If the water pressure is excessive, something will burst, or it will cause the flow to reach a maximum, due to the inability to pass more water.