Jet engines enable an aircraft to fly higher and faster. Turbines are also more reliable than piston engines, which can make flying safer, especially over water or rough terrain.
Jet engines compress air and mix it with fuel to produce thrust, just as a piston engine does. But in a turbine the air is compressed as it moves through a series of fan blades, then it is ignited. That hot gas expands greatly and is pushed out the back of the compressor, through another series of fans. Like water over a big wheel these exhaust fans are connected to the compressor, rotating it. That high-velocity air being pushed out the back is what pushes the jet forward.
Newer jet engines are efficient and feature a high bypass ratio. Through a large initial fan, they take in copious amounts of air, only some of which is mixed with fuel and burned. The rest is compressed and squeezed out the small back nozzle. By taking in more air the engine can produce the same thrust with less fuel burn.
Types of turbine engines
This is what most people think of when they think of a jet engine. Almost all modern commercial jet engines are turbofans, incorporating a high bypass ratio.
Turboprop engines are jet engines with the first fan stage in the form of a propeller. The drive shaft is often connected to a gearbox that allows the propeller to turn more slowly than the compressor stage. Turboprops are more fuel efficient than turbofans.
Primarily used on helicopters, turboshaft engines are turbines with a drive shaft that is connected to a fan in the back of the engine. This means the power drives a shaft that is connected to a gearbox that turns the rotors.