Rockets require a higher amount of fuel to operate. The hot gases come out in force from the back side of the rocket which further pushes the rocket forward to fly higher in the air. They can speed up after getting a speed of 28,000 km/h. More than billions of combustion elements exert force by which rocket flies higher and higher. When the fuel is used by the rockets completely, they fall towards the earth in some ocean or isolated areas away from human population.
So now, if you get a question on how rockets work, you can explain it by giving the example of the balloon.
(Courtesy: slideplayer.com)
https://www.youtube.com/watch?v=QQB1Iw3zJbc