Car reads "oil level system faulty"

I bought an oil level switch but don't know how to fix it or where anything is located. I tried looking up videos or something but nothing seems to come up. My car oil light have been on since I got it (July 2014) I got an oil change and still didn't work so I ask my father (past owner) and he said the mechanic broke the oil switch and never fixed it. Car readings says " PSI " and sometime 0. Any ideas if its something else?
p.S. Have not put oil pressure switch on, NEED HELP.