The first prophesy is that Macbeth is to "Beware Macduff." He should beware because Macduff will be the one to kill him.
The second is that "None Born of Woman" can destroy Macbeth. Macbeth now thinks he is invincible. However, Macbeth finds out in Act V that Macduff was "untimely ripped" from his mother's womb. So he wasn't officially "born of woman."
The last prophesy is about the woods making their way up the hill to his castle. He doesn't believe this could happen either. However, the men decide to cut down branches with leaves to camouflage their numbers as they make their way to his castle.