If you have a brand-new cast iron skillet you will need to season it before you can use it. Rub it lightly with vegetable shortening. Coat the interior where food will touch. Do not use vegetable oil as it will leave the pan sticky. Next, heat the pan in a 250 degree oven for 2 hours. It may be necessary to add extra shortening to the pan. Do not let it dry out; if it does then apply more shortening. Let it get stone cold and wipe out with paper towel.
If you find an old cast iron pan in the basement or at a garage sale, scour the pan with steel wool and then follow the above directions for seasoning the pan. Wash cast iron quickly with a little dish washing liquid. Don’t soak it for long periods of time or use a scouring pad. Always be sure to dry with a paper towel and then set on a warm burner to finish drying. Re season the pan as needed.