Define intertextuality, and what are three examples of how intertextuality helps in reading specific works?
I understand intertextuality, but what does the rest of the question mean?
To review, intertextuality is the using of another text to create meaning for another text. Essentially, an author, influenced by a text, uses the text/s to create a new original piece of literature. Given that the question does not refer to any of the works read, the answer will define general examples of intetextuality.
One example of intertextuality is Gregory Maguire's novel Wicked. The novel was inspired by L. Frank Baum's 1939 novel The Wonderful Wizard of Oz. Inspired by the omitted story of how the Wicked Witch came to be wicked, Maguire created a story which defined the Wicked Witch's beginning.
Another example of intertexuality is Arthur Laurents' West Side Story. Laurent was inspired to write West Side Story by William Shakespeare's tragic play Romeo and Juliet. There are similarities between Romeo and Juliet and Maria and Tony. Both Maria and Juliet have been forbidden to love the man they desire to love. Both novels end tragically for the historical "star-crossed lovers."
One final example of intertextuality is any literary text which adopted for film. Any filmatic adaptation which has been influenced by an original literary text is an example of intertextuality. The original text is read, interpreted, defined and adapted according to the allocated meaning by the writer.
Many examples of this exist: Kenneth Branagh's adaptation of Mary Shelley's Frankenstein, Neil Jordan's adaptation of Anne Rice's Interview With a Vampire, and Elia Kazan's adaptation of Tennessee Williams' play A Streetcar Named Desire.
Essentially, the question is asking how the knowledge of one text, which influences another, has helped one to understand the text in question. As defined above, one can see how texts shape other texts. This is how intertexuality helps one in reading. The effect is generally more subtle as themes, style, tone, minimalism, genre, etc., or literary period also influence texts that come later or in contemporaneous periods.