Rockets rely on the momentum or push that fuels (or “propellants”) create when they are oxidised. There are several types of propellants, and even different propellants are used in different moments of the missions of the ships… There are fossil-based propellants: these are liquids, hydrocarbons, like kerosene, which is mixed with oxygen for oxidation/combustion. There are cryogenic propellants: these are liquids that need to be at very loooow temperatures (lower than minus 200 degrees Celsius) to be kept as liquids, like H2 or methane, which are also mixed with liquid oxygen for oxidation and combustion. Hydrogen is currently the most efficient fuel, since it burns quite efficiently and generates a stronger impulse than fossil-based propellants.
If you are doing physics you will have come across Newtons laws of motion, and these can be used to describe the rocket launch. The rocket engine will allow the rocket to eventually accelerate so it can be launched into the sky and to move upwards the the hot exhaust gas is fired down and this represents Newtons 3rd law of motion that to every action there is an equal and opposite reaction.