The best way to season cast iron for the first time is to heat the oven to 450F, apply a thin layer of flaxseed or vegetable oil (my grandparents used lard) to the inside and outside of the pan, invert the pan on a baking tray, and place in the oven for one hour; turn the oven off and allow the pan to cool in the oven. The goal is to have the oil bond to the cast iron when heated to create a slick nonstick surface. Using too much oil can make the surface of the cast iron gummy, so only apply a thin coating.
After every time you cook, you should clean out the pan by wiping out any leftover food bits. If they aren't coming off, you can use a small amount of soap and water, and then make sure you dry out the pan by placing it over medium heat. If you take care of your pans, they can last for generations - I have my great grandparents cast iron from the early 1900s
Looking for cast iron pans? Thrift stores and estate sales are great places to find traditional pans and unique pieces. If you have any questions, I'd love to help! Please email Melanie@gatherculinary.com