Even though this is a text-based game, think of it as two-dimensional where you are viewing the level's floor from overhead.
Each floor is always rectangular in shape and is made up of a number of squares. At its edge there are walls; you can't move there. You can move to any other square, including the stairs, that isn't already occupied by another unit (only one unit can be on a given square at a time).
Here is an example of a floor map and key:
╔════╗ ║C s>║ ║ S s║ ║C @ ║ ╚════╝ > = stairs @ = Jon Snow (20 HP) s = Sludge (12 HP) S = Thick Sludge (24 HP) C = Captive (1 HP)