A properly working engine oil pump is essential to keeping your engine lubricated and operating properly.
When your cars oil pump fails then the oil in the oil pan will not be able to get pumped out of the oil pan and move around through your engine to lubricate it properly.
Without proper lubrication of the engines moving parts the engine will create friction and when those parts get too much friction the parts will seize up and your engine will stop working altogether.
You might first notice that your engines main bearing is going bad due to loss of lubrication by a loud grinding or squealing noise while the engine is running.
Eventually your engine will completely seize up without proper lubrication.
So if you notice a loss in oil pressure the engine needs to be checked out as soon as possible before your engine stops working and seizes up.