BattleMaps works with a succession of phases overlayed on an unchanging background. You can work with phases by selecting the menu item 'Phases':

Each phase represents a snapshot, or a moment in time, of the battlefield. It behaves like an invisible layer sitting on the background layer and contains all the units and other objects added to it.
You also annotate each phase with a title and details of the action at this point.
Examples of phases of a battle could be different times throughout the day of the battle, e.g. 9:00am When the forces arrayed themselves for battle, 11:00am When a flank was turned, 12:30pm - The rout. Alternatively, if the map illustrates an ongoing campaign, each phase might represent a day, a week, a month.
When the BattleMap is finally finished, each phase will be presented as an individual map, either :
For more information on working with phases, see:
and, of course :