Here's how it works:

1. Burning Fuel: A rocket engine burns fuel, typically a combination of liquid hydrogen and oxygen, creating hot, expanding gases.

2. Nozzle: The hot gases are channeled through a nozzle, which accelerates them to a high velocity.

3. Newton's Third Law: As the gases are expelled out the nozzle, they push against the rocket in the opposite direction, creating a forward thrust. This is a direct application of Newton's Third Law of Motion: for every action, there is an equal and opposite reaction.

Important Note: The rocket doesn't actually push against the air. It can fly in a vacuum, like in space, because the thrust is generated by the expulsion of the hot gases, not by pushing against anything.

Additional factors:

* Gravity: The force of gravity is constantly pulling the rocket back down to Earth. The rocket's thrust must be strong enough to overcome gravity and accelerate upwards.

* Aerodynamics: The shape of the rocket and its fins help to control its flight and minimize air resistance.

In summary: A rocket flies because its engine expels hot gases at high speed, generating a force called thrust. This thrust overcomes the force of gravity and propels the rocket upwards.