Here's how it works:

1. Burning Fuel: A rocket engine burns fuel, creating hot, expanding gases.

2. Expulsion of Gases: These gases are expelled out of the rocket's nozzle at high speed.

3. Reaction Force: The rocket pushes the gases out (action), and the gases push back on the rocket (reaction). This reaction force propels the rocket forward.

Think of it like this:

* Imagine you're standing on a skateboard and you throw a heavy ball forward. The ball moves forward (action), and you move backward (reaction).

* A rocket is essentially doing the same thing, but instead of throwing a ball, it's expelling hot gases.

Key Point: Rockets don't need anything to push against in space to move. They generate their own thrust by expelling mass (the hot gases). This is why they can travel in the vacuum of space.