Crankshaft position sensor

My car won’t fire, was running fine then I parked it went to start it again later and it wouldn’t fire. Thought I ran it out of gas so we put more gas in it still wouldn’t fire. We were told it could be the fuel pump so we replace that and it still wouldn’t fire So we replaced the sparks and wires and did an oil change. Car still will not fire so after conducting some tests we feel it may be the crankshaft position sensor but we are not sure. Any information on what it could be or where to find the crankshaft position sensor would be greatly appreciated.