People often wonder how a rocket can go through space with nothing to push against.
It works because the rocket is actually always pushing against itself. The fuel is fed through to the 'combustion chamber' at the bottom of the rocket, where it is mixed with an 'oxidiser', and burnt. The explosive force of the burning fuel is the same in all directions, but the outlet nozzle directs it. The force pushing out on the two sides of the combustion chamber is equal, and so they cancel each other out. But the force upwards on the top of the combustion chamber, and the entire rocket, is not cancelled out - the downward force of the explosion escapes through the nozzle.