There are a number of pistons inside the engine depending on the design, 4 to 12 cylinders usually. The pistons are now connected to a crankshaft through a connecting rod. Pistons fire consecutively to rotate the crankshaft inside the engine block.
The oil pump pushes oil through the oil filter and then supplies oil to vital engine parts including the crank and camshaft, cylinder walls and piston rings, valve train, cam lifters and the timing gears or chain. Motor oil is used to lubricate and cool the internal engine parts. Oil is pumped up through the engine, then it returns to the bottom of the engine and is gathered in the oil pan.