Whereas jet aircraft use the atmosphere both as a source of oxidant and of mass to accelerate reactively behind the aircraft, rocket aircraft carry the oxidizer on board and accelerate the burned fuel and oxidizer backwards as the sole source of mass for reaction.
Liquid fuel and oxidizer may be pumped into a combustion chamber or a solid fuel with oxidizer may burn in the fuel chamber.
Whether liquid or solid-fueled, the hot gas is accelerated through a nozzle.