Watt

Watt (W) is the international standard (SI) unit of measure for power. By scientific definition in physics power is the amount of work performed in a unit of time; in SI that would the the joules (J) of work performed in one second (s) period of time.
1W = 1J / 1s
And one joule is the work performed when a force of 1 newton (N) moved an object at 1 meter (m) distance.
So 1 W wold be applying that 1 N force to move an object with a speed of 1 m/s.
It, the power, is basically the rate (speed) at which amount of work is being performed (amount of energy is being transferred).
This is in terms of mechanical energy.
In terms of electricity the watt (W) is equivalent but can be calculated easier if looked upon as the multiplication of voltage and current.
1W = 1A x 1V
An electric energy source, a battery, a generator, a solar panel, when connected to certain load circuit generates as much power as much is the mathematical product of the current it produces and voltage it maintains. Power (W) = Current (A) x Voltage (V). This is for generated power. Same goes for consumed power – a load (an electric bulb, an electric heater, any electrically powered device) has power consumption of the voltage it operates under times the amps it uses.
Since the electric and W are equivalent. If a device that generated 1W of power works for one 1 s – it generated 1 J of work/energy in that second. In electricity instead of joules (J) Ws (watt second) is used more often for amount of energy (generated, transferred or consumed). And in fact the though the Ws is the SI main unit, in commerce and practical applications the Wh (watthour, watt-hour) is the more commonly used unit of measure. 1 Wh = 3600 Ws. 1Wh is the energy a device generated, transferred or consumed when for one our it was working at 1W power (1V x 1A).
Since in practical applications Wh is again too small in many cases kWh (=1,000Wh) is used and industrial applications MWh (=1,000kWh) is used.
The consumption of electric energy of a regular home in the US ranges on average around 1 – 3 MWh per month.
So if we have to recap, the connection between watts and watt-hours – a very often confused pair of units is the time. Watts multiplied by time is watt-hours. A device using 100W power working for 10 hours will consume 1,000Wh = 1kWh. A solar photovoltaic station with peak power 100kW working for 4 hours at peak (for the day) will generate 400kWh.