The witches make predictions for Macbeth and Banquo in this act, saying Macbeth will become king and Banquo’s descendents shall become king but not himself
Macbeth conspires to kill King Duncan, and eventually does, stabbing him in his sleep
Macbeth fears Banquo because he thinks he knows too much of his crimes, as well as the witches predictions stating that Banquo’s descendents shall reign as kings, so he hires some thugs to kill Banquo and his son, Fleance. Banquo dies but Fleance escapes
Macbeth seeks the witches for council, no longer afraid of them. They show him four apparitions: the first says to beware Macduff. The second says that Macbeth will not fall to any man born of a woman. The third says that Macbeth will not fall until Birnam Wood comes for him. The fourth appear as 8 kings, who are Banquo's descendents. Macbeth then has Macduff's family killed, to destroy his line of inheritance.
Malcom and Macduff side with Englishmen to overthrow Macbeth. They disguise themselves with branches from Birnam Wood, and it looks like it is moving. Macbeth's army gets beat up by the English army while Macbeth and Macduff fight, and Macduff reveals that he was cut out of the womb before he could be naturally born. Thus, Macbeth is defeated by Macduff and malcom is crowned king.