The power rating of an appliance tells you how much energy it transfers each second. It is measured in watts (W), and one watt is one joule per second. The equation is power = energy transferred ÷ time, or P = E/t, which can be rearranged to E = P × t.
A kettle rated at 2000 W (2 kW) transfers 2000 J every second from the mains to the thermal store of the water. A 100 W lamp transfers 100 J every second, so in 60 s it transfers 6000 J. A motor in a washing machine transfers energy to the kinetic store of the drum.
An appliance with a higher power rating transfers more energy each second than one with a lower rating. A hairdryer or a heater has a high power rating because it must transfer a lot of energy to heat quickly. A phone charger has a low rating. Power is not the same as total energy, because the total depends on how long the appliance is switched on.