The brood frames are where the bees store nectar and pollen for their immediate use. It's also where the queen lays the eggs that will hatch first into larvae and then metamorphose into new bees. There are lots of slightly different sizes of frames. The beehaus uses these deep National frames which are the most common size used in the UK. Every beehaus is shipped with 10 deep national brood frames (often called 14x12 frames) but you may want to invest in some spares.
Please note these come unassembled and they do not come with foundations. The brood foundations can be bought as a pack of 10 too.