Restart the Dungeon Generator.
Width: This is how wide the dungeon is.
Height: This is how tall the dungeon is.
Sparseness: This defines how 'sparse' the dungeon is. A dense dungeon has only one square separating all corridors. A sparser dungeon makes the corridors further apart and also has the effect of reducing the number of corridors.
Randomness: This determines how often a corridor bends. A dungeon with a low percentage of randomness will have many long, straight corridors with few bends in them. A very random dungeon will have very windy corridors.
Deadends Removed: This defines what percentage of deadend corridors are 'removed'. This is typically done by connecting the end of one corridor with the next nearest corridor and may form a loop at the end of the hall if the deadend is reconnected to the same corridor.
Level: This is the level of the dungeon to generate and determines the difficulty of the monsters encountered in the dungeon.
Random Seed: Every dungeon that is generated has a random seed value associated with it. After generating a dungeon, the seed value for that dungeon may be found by looking immediately below the map. If you were to put that number into this field and set all the parameters the same way they were the first time you generated that map, you would get the exact same dungeon again. This is useful for debugging and for sharing dungeons with friends.
Room Count: This determines how many rooms exist in the dungeon. It is a relative value, based on the size and sparseness of the dungeon. A dungeon with 'too many' rooms will be very crowded, with very few corridors but lots of doors. A dungeon with no rooms will be all corridor (a maze, essentially).
Room Width: This is how wide the rooms in the dungeon are. You specify the minimum and maximum widths, in 'squares' (i.e. grid squares).
Room Height: This is how deep the rooms in the dungeon are. You specify the minimum and maximum depths, in 'squares' (i.e. grid squares).
Secret Doors: This is specified as a percentage of the doors in the dungeon that should be secret doors. If the dungeon has no rooms, it will have no doors and thus no secret doors, either.
Concealed Doors: This is specified as a percentage of the doors in the dungeon that should be concealed. If the dungeon has no rooms, it will have no doors and thus no concealed doors, either.
Grid Resolution: This is how large the squares are on the map. Specifying a smaller grid resolution will make large maps somewhat smaller and specifying a larger grid resolution will make them larger.