Once you have made a selection of ships using the toolbar or the fleet book, use a map cursor to command it. The map cursors allow you to assign your selected fleet in four different ways: movement to another sea zone plus three kinds of missions.
To move the fleet, click on a new sea zone with the ship's wheel cursor. This cursor does not appear in the fleet's current sea zone. If the new zone is out of range you see a red slashed circle cursor; you cannot move the fleet that far in one turn.