Skillets can be made from different types of material. Stainless steel, aluminum, and cast iron are common options. Some skillets are made from a combination of aluminum and stainless steel. Aluminum pans that have a thin gauge (read: not very thick) aren't the best choice since they are more likely to warp.
They are perfect for searing because of the way they disperse heat. They’re also perfect for cooking meats and fish.