In the English test you have to answer one question about Shakespeare. This question will be about two extracts from the play you are studying. You need to know the two extracts well, but you should also have a good idea of the basic plot of the play.
This revision bite gives you a summary of Macbeth and shows you how the two extracts fit into the overall story.
Don't try to remember every detail of the play. Instead, learn the basic story and then concentrate on the characters and their relationships with each other. You should also think about how an audience will react (remember, it was written to be performed in a theatre) and the themes it deals with, such as betrayal, ambition and fate.