Steamed: If you order tamales labeled as steamed, this means that they have already been cooked for you. Reheating is your best option for leftover cooked tamales. They can still be put in the fridge or freezer depending how long you want them to last.
Frozen: If you order tamales labeled as frozen, it means the masa (corn dough) is uncooked, this means that the tamal has not been steamed in which the masa is still raw. Everything inside the tamal is cooked, however, so if you order uncooked, you need to steam them to cook the masa. Often times, the uncooked tamales will be cold/frozen but if they are not, it means the tamales were made a couple hours before you got them.