The engine lubrication system consists of an oil cavity (where the oil is stored), the oil line (like a blood vessel that carries around the body), the oil pump (like the heart) and the oil refining (like the kidneys, eliminating residues before being pumped into the engine).
When the oil is pumped through the engine, under pressure, it stays in the engine with a special lubricating film (oil film), creating a smooth surface (or sliding effect) over the areas it passes through. The main job of the oil film is to ensure smooth engine parts movement while minimizing component friction and wear, thereby increasing engine efficiency and longevity.
Also, one of the other important roles an engine oil plays is heat transfer. When the engine is running, the heat is radiated large, so the oil helps to transfer heat away from the lubricated parts of the engine such as bearings, pistons, valve bodies, cylinder holes … during operation.