What is a heat pump? why does it need to put in external work? (i have 2 minutes left of a timed test)

Aheat pump is a device that transfers heat energy from a source of heat to a destination called a "heat sink". heat pumps are designed to move thermal energy in the opposite direction of spontaneous heat transfer by absorbing heat from a cold space and releasing it to a warmer one. a heat pump uses a small amount of external power to accomplish the work of transferring energy from the heat source to the heat sink.

Answerit increases at a steady rate;