Check engine light came on. Is running a little rough....could it be bad gas? on 1998 Oldsmobile Aurora

Codes P0171, 0174, 0300 came up. How do I find out what they mean? Gas cap has been checked and is good.

Asked by for the 1998 Oldsmobile Aurora
ck for vac leak and then misfires.vac leak may be causing misfires