Thermal expansion of the combusting gases in the rocket nozzles (bottom of the rocket) pushes them against the outside air, and the equal-and-opposite reaction is to push the rocket upward.
Rockets exert force at the upper part of the combustion chamber. This pushes the rocket forward.
it is a thrust
force applied by us
the rocket pushes on the ground and the force of the fuel igniting pushes the rocket up
Its called Inertia
'Thrust' pushes against it from the rear, and 'drag' pushes against it from the front.
Force of Inertia
Rockets provide force that can propel ships forward, even in the near vacuum conditions of space. Propellers can provide force only in a substantial atmosphere.