How does a steam turbine differ from a steam engine?

The main difference is the maximum revolution per minute of the power cycles that both could provide. There is a limit for the number of cycles per minute that could provide with a steam driven reciprocating piston, inherent in its design.

Steam turbines rotate in the currents caused by the hot water vapour. They form part of a closed water cycle in which water condenses and is then heated until it evaporates again. Steam turbines therefore do not come into contact with the fuel deployed and work at temperatures between 500 and 650 °C. Several steam turbines are often arranged in a row so that - configured for high, medium and low pressure - they are able to optimally convert the respective steam pressure into rotational movement.

Gas turbines on the other hand rotate directly in the hot combustion gases. With temperatures up to 1500 °C, these gases are much hotter than those in steam turbines. For this reason the blades are cooled with air that flows out of small openings and creates a "protective film" between the exhaust gases and the blades. Without cooling, the blade material would quickly wear out.