In many aircraft, the powerplant includes both the engine and the propeller.
The primary function of the engine is to provide the power to turn the propeller.
Accessories mounted on, or connected to the engine generate eletrical power and create a vacuum source for the gyroscopic flight instruments.
And in some airplanes provides heat for the cabin/cockpit.
The PROPELLER, that is mounted on the front of the engine, transltes the rotating force of the engine into a forward-acting force called thrust that helps to propeller the aircraft through the air.