Jet engine theory can be summed up in these four words:

Suck, Squeeze, Bang, and Blow.

This describes the operation of most aviation engines. The suck of a jet engine can be compared to the intake stroke of the piston. squeeze parallels the compression stroke. Bang is the ignition, and blow is the exhaust. Piston engines carry out these actions in sequence but the jet engine performs all operations simultaneously.

All aviation jet engines work in the same basic way - they accelerate a volume of air backwards. That rearward acceleration of the air results in an equal and opposite action on the engine and it is accelerated forward. Since the engine is bolted to the airplane, forward motion is achieved.

Newton's second law states that a force is equal to the product of a mass and the amount the mass is accelerated. If you take a large mass and accelerate it a small amount, you can achieve the same results as taking a small mass and accelerating it a large amount.