Pan dressed means the fish has been eviscerated and scaled if necessary. Often the head and fins have been removed and the fish is ready to cook. Fillets are the strips of flesh from the sides of fish. They are boneless and may still have the skin on one side. The fish dealer will usually remove this skin for you if asked.
Steaks are cross section slices of large dressed fish such as salmon or halibut.
A piece of the backbone is usually still present in the steak, but easily removed after cooking. Do not hesitate to ask the fish dealer to allow you to smell the fish before purchase. It should smell fresh and mild, with no strong fish smell. Before cooking any fresh fish rinse completely in cold running water and pat dry. Fish can be sauted, grilled, broiled, poached, or baked.