Crew Orders are used to move Crew members around on the ship. Using one Crew Order allows a player to move one Crew member from anywhere on the ship to any other valid location on the ship.
When moving a Crew member to a position On Deck, the Crew member can be placed in any Zone, except that there can never be more than three miniatures, counting both Crew member and On Deck enemies. Some Zones contain Nodes that Crew members can man and which are relevant for other actions; manning Navigation Nodes and the Crow's Nest Node improves the effect of the Navigation Order, and manning Artillery Nodes makes it possible to use Artillery Orders. The blank Nodes give no benefits, and are usually the place where On Deck enemies appear when the spawn.
When moving a Crew member to a position Below Deck, the Crew member can be placed on an empty slot, or on an Improvement. Some Improvements have one or more Crew effect spaces, and the Crew member can be placed either on such a space (possibly triggering the effect), or just on that Improvement but not on any Crew Effect space.
In order to trigger a Crew effect space, it must be a space that has a triggered action (usually something that has a direct effect on the Crew members that moved there), and the Crew member that moved received a Fatigued marker. If the Crew member is already Fatigued, the action can't be triggered, but it's still possible to move the Crew member to that space. Fatigue wears off at the start of the Player Phase, so this limits each Crew member to triggering one Crew Effect per turn.