What is the purpose of the Oil Sump thats located under the crankshaft?

The sump with the screen in the bottom of the oil pan collects the oil before the vacuum from the oil pump pulls the oil from the sump pick-up tube into the oil pump.

The sump is NOT the oil pump!

Oil gets pumped through oil passageways in engine. Oil that gets to cylinder head will drain eventually down into the oil pan. There is an oil pick-up at the end of the oil pump, that gathers this oil and pumps it through the engine AGAIN! Some engine have a different kind of lubrication system that sdoes not include an oil pan per se, It is used in racing and where the car tips at severe angles to prevent dry running of engine bearings.

It helps keep the bearings lubricated in the bottom end of the motor and having a number of quarts keeps the oil pump circulating enough oil to keep the top lubricated too.

It pumps the oil up to the top of the engine where it trickles down into all the parts that need to be lubed.

Function Of Oil Sump