Inside hive boxes are frames and foundation on which the bees can build their comb for storing brood, pollen, and honey. A frame is simply four pieces of wood to securely hold the foundation in place. Frames are designed to be easily removable for inspecting the hive and harvesting honey. Beekeepers can reuse frames and comb for a long time if it is cared for. New foundation is marked with small hexagons to help the bees as they draw out comb - not that the bees need it! It just helps to keep the hive orderly for the beekeeper's benefit.
Make sure you are choosing the right size foundation and frames for your hive - medium frames do not fit in deep boxes, and vice versa.