I need to explain the importance and role of the witches and the prophecies to the outcome of the play. Did they control Macbeth and drive his...

The Weird Sisters purposely try to manipulate Macbeth, engaging his trust, and then deceiving him into believing that his ascension to the throne is all but guaranteed by fate, igniting his ambition to be king.

Duncan names Macbeth the Thane of Cawdor at the end of Act 1, Scene 3; therefore, when the Weird Sisters "predict" that he will become Thane of Cawdor, it has actually already happened -- Macbeth just doesn't know it yet.  Therefore, they appear to be telling his future when they are really just telling him some information he doesn't have yet.  Then, when Angus and Ross tell him of his new title, it appears to confirm their accuracy and honesty.  However, the fact that they seem to be good and honest to Macbeth is actually a clue that they are truly the opposite because, in the first scene, they admitted that they were going to make good things seem bad and bad things seem good when they say, "Fair is foul, and foul is fair" (1.1.12).  However, because the first of the witches' "prophecies" seems to have come true, Macbeth thinks, "If chance will have me king, why, chance may / crown me / Without my stir" (1.3.157-159).  He didn't have to do anything to make the first of the predictions come true, so he hopes that it will be the same with the second.

Later, the witches purposely deceive Macbeth, appearing to give him assurances that he will be safe from death, but these assurances turn out simply to be enigmatically-worded statements of fact.  The apparitions that the sisters conjure tell Macbeth that "none of woman born / Shall harm Macbeth" and that "Macbeth shall never vanquished be until / Great Birnam Wood to high Dunsinane Hill / Shall come against him" (4.1.91-92, 105-107).  It sounds as though they are saying that Macbeth is basically invulnerable since everyone is born of a woman and because the trees cannot get up and move.  However, there are some loopholes in these statements that Macbeth fails to consider (which is what the witches seemed to have hoped for).  He feels supremely confident at this point, and, as Hecate said, "you all know, security / Is mortals' chiefest enemy" (3.5.32-33).  Macbeth's confidence makes him a little careless, and he fails to consider the other ways in which the sisters' statements could come to fruition.