eNotes contains an abundance of information about Macbeth. You might begin by clicking on the reference links below. The Summary will give you an overview of the whole play. The Character Analysis will discuss most of the important characters. You will need to know something about Macbeth, Lady Macbeth, The Three Witches, and Macduff. Banquo is also somewhat important. If you know something about these characters, you might be able to get through the exam.
The theme is about ambition. Click on "Themes" in the Study Guide to get an idea of what is motivating the main character and his wife. His ambition leads to his ruin. That is the moral. Macbeth is an honorable man at the start of the play but he becomes dishonorable and a tyrant because of his ambition. His wife plays an important part in the early acts. She goads him into killing King Duncan. The Three Witches, also called the Weird Sisters, also play an important part because they make Macbeth think it is his destiny to become king and that anything he does is permissible.
Macbeth is killed by Macduff in the last act.