An engine puts all of its power in a propellor. The propellor accelerates a mass air in one direction, and by doing so, it creates thrust in the opposite direction. The exhaust gasses of the engine can also provide some thrust.
Air passing through a jet engine is heated up .
The hot air expands, and accelerates in one direction. By doing so, it creates thrust in the opposite direction. The accelerated mass exhaust gasses is not only consisting of air, the mass of the fuel is also a significant part of the accelerated mass. Don't Combine lift thrust and forward thrust. Use a large mass to repel on.