A blockhouse is a small, strong building used as a shelter from enemy guns. Soldiers hide in it, and they may shoot from it. It is often of heavy timber or later of concrete, with thick walls and small openings. The English word is block + house, a piece-by-piece copy (a calque) of German Blockhaus. It belongs to military and history English, not to everyday talk about homes. In some places people have also used it for a strong wooden house, but the sense you are learning is the little fort-like shelter. It is not an apartment block, and it is not a house built of children’s blocks.