The protagonist of William Shakespeare's Macbeth is an ambitious soldier named Macbeth who is rewarded with a title and land for his valor and loyalty to King Duncan of Scotland. Just before this promotion, three witches predicted that this would happen, so now Macbeth believes their other two predictions: that Macbeth will be king and that no one "born of woman" can kill him. His trusted friend Banquo is present for all of this and receives his own predictions from the witches.
Back home, Lady Macbeth gets the news from Macbeth about the witches' predictions and immediately wants to her husband become quick more quickly (though Macbeth is not so sure, deciding that if he is going to be king, it will have to happen naturally). Duncan comes for a visit with his loyal and trusted subject on whom he has just bestowed a title (Macbeth), and Lady Macbeth shames her husband into plotting Dincan's murder. She wants to kill Duncan but cannot bring herself to do it; Macbeth does the deed and now the trouble begins.
The Macbeths blame Duncan's murder on the king's two sons; they flee to avoid the accusations. Macbeth becomes king, but he is troubled by his guilt--though it does not stop him from killing Banquo to ensure that he can stay in power.
Things go quite badly for Scotland with the Macbeths at the helm, and both of them suffer from their guilt as others gather armies and try to save Scotland. Killing has become easier for Macbeth, and he foolishly relies on the witches' predictions that he cannot be harmed. This is a mistake.
One of the sons comes back with an army and Macbeth is vanquished in a way that makes the ambiguous prediction correct.
The primary theme of the play centers on the Macbeths' ambition; however, it is the witches who complicate matters in this play. “Confusion now hath made his masterpiece.”
For a more detailed summary, see the eNotes link below; however, reading the play is important to capture the intricacies of the plot as well as the questions Shakespeare raises about human nature.