Click on the empty tiles to the left to construct buildings, use them to defend your base from enemy and to produce units to attack them. All structures are upgradeable, which makes either them or units they produce more powerful.
Guide your Knight to each level's exit by drilling away the blocks he stands on, and letting gravity take effect. By rotating the entire game board, you can guide him anywhere you wish; into confrontations with the monsters that dwell in the dungeons.