A jet engine does not create a thrust force by pushing exhaust gases against atmospheric air. It is a reaction engine that increases the energy of the gases that go through it to produce thrust.
It can do this courtesy of Isaac Newton's second and third law of motion (guy with the apple). To recap those laws:
Force = Mass x Acceleration (F=Ma). A force is produced when a mass of
air is accelerated. This also means that a force is produced when the
momentum of the air is increased.
A jet engine
increases the momentum of the air that goes through it. This can be stated
We can show the above in a practical way, we can calculate the thrust produced by an engine as follows. Add together all the positive forces on the engine internal surfaces. Add together all the negative forces on the engine internal surfaces.
The net thrust is equal to total forward forces minus total rearward forces. See below for an example.