If you run the car in cold weather, the fuel mixture is richened to warm engine, excess fuel not burned can get into the oil. Also, if you have a car that starts hard-long cranking or has a misfire; the excess gas that is not burned will get into your oil.
Many things can cause this, some are, from a short driving cycle that doesn't allow the engine to fully warm up, to a faulty fuel pressure regulator, to leaking fuel injector/s or a carburator float bowl being overfilled, to worn engine parts, like piston rings, valve guides, faulty spark plugs resulting in poor fuel burn ect, ect.
Basically it's gasoline getting from the top of the engine, into the bottom of the engine, where the oil sump is.
Gasoline in the oil isn't good for it, or the engine, as it dilutes the oil & robs it of it's lubricating properties, resulting in accelerated engine wear & bad engine deposits.
Best to change the oil & filter right away, review all the listed ideas & have the most likely checked out by a pro you trust.
If your cars mechanical condition is ok, but your driving cycle is short, after changing the oil & filter, try changing your driving cycle, or by taking your car on a weekly 20 mile interstate round trip, to warm the engine & oil up competely, to evaporate condensation & any gasoline thats found it's way into the crankcase oil sump.
Your ride will love you for it & the gas oder in the oil, will likely take a hike!!!!
your car is not good mechanically or u would not be getting fuel in oil. take it to a REPUTABLE mechanic and get it looked at .problem may be small and easy to fix. the longer you wait the worse it will get