Macbeth orders two murderers to kill Banquo and his son Fleance.
The murderers succeeded in half of Macbeth's orders and killed Banquo. They couldn't kill Fleance because he fled the scene.
Macbeth is seeing Banquo's ghost and the people who are witnessing Macbeth's hallucinations think he is going mad. Lady Macbeth assures them that this is normal for him and he has acted out like this for as long as she can remember.
Macduff kills Macbeth and finally defeats him after he tells Macbeth that he "was from his mother's womb untimely ripped."
Macduff enters carrying Macbeth's head while Malcolm invites everyone to watch him be crowned king of Scotland at Scone.