If the mist bank is not finished, place as many ghosts on the tile you just placed as there are ghost symbols on it.
If you expanded at least one mist bank (i.e. matched at least one side of the tile you just placed with mist already on the board), then you place one fewer ghost on the tile. If the tile only shows a single ghost, then you don’t need to place any ghosts.
First you place this tile . You see 2 on it and place 2 ghosts on it. On a later turn, you place this tile expanding the mists. Since there is only 1 on it, you don‘t need to place any ghosts. Well done!
Important: If, at any time, there are fewer ghosts left in the supply than you need to place on a tile, you immediately lose the game (see 'Game End').
You can never place a meeple onto mist. You may, however, place one onto an unoccupied road or city on the tile, as per usual (or, in later levels, into a castle – see Level 2: Castles).