To clean a cast iron skillet, boil a bit of plain water in it to loosen burned on food, rinse and let it dry. Rub with a bit of vegetable oil, wipe off excess and heat till it just starts to smoke. Turn off heat and let it cool without wiping.
Never cook anything with acid (vinegar, tomato sause) in it. Cast iron is for cooking with fat. After you brown meat in it, you can make a great gravy by browning some folur in the leftover fat, then adding water a little at a time till it's the right thickness. (Thickening requires bringing the mixture to a boil.) Add seasonings.