When Actors move in the game it is normally an Automatic Action where the Player simply states their desire for their Actor to move and it takes place.
Requirement: in order to move, an Actor must have non-zero FIT and AGI.
Game Mechanic: technically, when an Actor moves, they are taking a Fitness Action and bidding FIT vs. the target of their action being the surface they are walking on (Abstract Actor).
Difficulty: when moving over a normal flat surface always assume Difficulty 1 (a child could accomplish it), meaning that an Actor must bid 1 FIT to move over it successfully. If moving over more difficult terrain, the GM may determine that the terrain Abstract Actor is bidding more FIT in opposition to the Actor.
During a Conflict when an Actor moves during a Conflict, because their target is Abstract, their Action during that hand never scores damage vs. any other Actor. However, their bid on the movement Action does count toward determining the Margin of any other Actor trying to damage them (i.e. they are assumed to be reacting defensively