turn ignition on and off have someone listen in trnk they should be able to here it kick on or raise hood look on the fuel rail they will be a valve like on a tire stik something in it an release all...
When the old one becomes noisy, weak, or stops pumping fuel altogether. Assuming the fuel filter is not clogged, the fuel pump fuse is not blown, and the fuel pump relay is good.
You will have an idea that you need a new oil pump if it no longer puts out adequate pressure to lubricate the engine bearings. Use an actual oil pressure gauge to check the oil pressure, the dash...