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the oil pump was a very interesting piece of machinery,  in a nutshell, it works by a gear which sits inside a slightly larger inverted gear, and as oil passes through into the clearances, it is basically transferred to another point.  It is important to remember that the oil pump itself does not create any oil pressure, only flow, and the parts inside the engine that use oil create the oil pressure, by limiting flow.

There are three main types of oil pumps, there is the gear pump, which is very common, twin gear pump (A.K.A. cresent pump), which works very similarly to the supercharger, and the rotary pump. All of these mechanisms work very similar to each other, with the same goal of being able to create a flow for oil to flow around the engine.  They all have something called a pressure relieve valve, which acts like a wastegate in a way, if too much oil pressure is built up, the oil pressure pushes down a valve and flows out back into the sump.