Answer
Every heat engine receives heat flowing in from some source, converts some of the heat to useful work, and expels the remaining heat to its environment.
Work Step by Step
For example, a car's engine receives heat (from a high-temperature internal combustion chamber where fossil fuels are burned), turns the crankshaft that drives the wheels, and exhausts some heat from the tailpipe (to the low-temperature environment).
This is discussed on page 344.
