"No!" shrieked my mother as teenage me scrubbed her prized cast iron pan with soap and water, "What are you doing? You'll ruin it!"
I didn't realize it at the time, but cast iron needs special treatment in the kitchen. You might soak a nonstick pan in the sink, wipe it down, and stick it in the dishwasher, but doing that to cast iron might damage it, or at least render it basically useless for cooking. But what's the big deal about cast iron pans? What do you need to do? Why can't you wash them the same way?
Cast iron requires what the kitchen-savvy call 'seasoning.' This doesn't mean that you coat it in spices or culinary herbs, but before you can use it, it does need special prep. Seasoning, in this case, actually refers to using oil or another fat to coat the pan and bake it. Doing this creates a layer upon which food can lie, avoiding contact with the actual iron of the pan. Iron, while an ideal cooking material, rusts easily and can create a weird aftertaste in your food. The oil helps prevent rust and helps protect food from a metallic aftertaste.
So how do you do it?
First, clean the pan. Soap and water is fine this time. Afterward, dry it as thoroughly as possible with a clean cloth. Next, put about 2 tablespoons of oil or fat in the pan. Vegetable oil will work just fine! Then, coat the bottom and inner sides of the pan completely with the oil or fat. Then, bake it at about 375-400°F for approximately an hour. Let it cool completely, then wipe it out with a clean cloth. This is the best way to preserve the oil coating from then on, as well: you should avoid using soap and water after seasoning the pan!