The power of a device is the rate at which it transfers energy. It is measured in watts (W), where one watt is one joule per second. The power depends on two things: the potential difference across the device and the current through it. Power = potential difference × current (P = V × I). A motor with 12 V across it and a current of 3.0 A has a power of 36 W. A kettle element with 230 V across it and 10 A through it has a power of 2300 W.
A p.d. is the energy transferred for each coulomb of charge that passes, so one volt is one joule per coulomb. The charge that passes is the current multiplied by the time, Q = I × t. The energy transferred is E = Q × V. Putting these together gives energy transferred = power × time (E = P × t).
For the 12 V motor with 3.0 A running for 60 s, the charge is 3.0 × 60 = 180 C. The energy transferred is 180 × 12 = 2160 J, which agrees with 36 W × 60 s = 2160 J.
A bigger p.d. or a bigger current gives a larger power, so more energy is transferred each second. A device of higher power transfers more energy in the same time.