As noted above, the literal battle that the witches discuss is the war between Scotland and Norway.  Duncan's army has been dispatched to fight against the Norweyan army, and later the audience finds out that Banquo and Macbeth have played major roles in the battle.  The witches always speak in paradoxes, and the above quotation is an example of one:  "When the battle is lost and won."  On a first reading, it seems impossible for a battle to be both lost and won, but perspective proves the statement to be true:  one side of the battle will win, while the other will lose.  In this case, Scotland came out of the battle victorious over Norway.  And the witches do meet once the battle is over when they are confronted by Macbeth and Banquo who are on their way home from the war.

Figuratively speaking, the hurly-burly refers to the moral battles that will continue to wage throughout the course of the play.  The witches meet again when Macbeth goes to see them to get more answers about the safety of his place as King.  At this point, it seems that Duncan has "lost" while Macbeth has "won," but the sides of good and evil are not so clear.