see the below picture, we can clearly see that the engine is of an aeroplane, the question arises how does they work.... let me explain, once a aeroplane is on the ground, start the engine as u start the engine the APU will throw the air into the engine by the help of air duct connected to the engine, that air has to gone through different phases, first it goes to air compresser, which compresses the air making the air temperature rises and allow it to moves into the combustion chamber, here the fuel is thrown by all the nozzles and the spark plug is used to ignite when the compressed air went to chamber it burst out there and allowed to move out from the other side, as the compressed air along with that burst moves the compressed air wanted to expand thus making another burst inside and making the turbine( on the extreme left ) moves because of the pressure as the turbine moves it allows the outter most fan to move and move, since the turbine and outter fan are connected in the same series, when the turbine moves it allows the outter most fan to move also due to same shafts as this fan moves it allows more air to get in and out and making the engine runs, this thing happen continiously till both the turbine and outter most fan attains the same RPM, once it done the flow of the air becomes constant and things are stable, that is why when engine starts the consumpution of fuel increases and as it goes up it goes to ecnomical because of the air pressure and all.
This working applied to all jet engines..