Two major themes are right in the title. Pride, meaning being so self-congratulatory about one's strengths and attributes (often wealth, or social standing) that one does not admit any weaknesses. In essence, one is unable to empathize with others. And Prejudice, meaning forming opinions about people or things before having any real knowledge (or only surface knowledge) about them. These opinions are most often negative and based upon previous experiences.
Elizabeth Bennett and Mr. Darcy are both meant to, at various points in the story, exhibit both of these attributes. The other characters in the main and subplots also reflect these themes.
I can't write a paragraph for you because it's your assignment, but I can give some information to get you started. According to the enotes study guide on Austen's Pride and Prejudice, numerous themes are revealed in the novel:
- Prejudice and Tolerance
- Change and Transformation
- Wealth and Class
- Rights, Status, and Education of Women
- Personal Autonomy
- Irony and Satire (used by the characters as well as in the novel as a whole)
A paragraph or two is easy. Pick one and find evidence that it is revealed in the novel.
If you choose prejudice, for instance, simply find examples of people being prejudiced. Look for reverse prejudice, too: those of a lower economic class for instance, prejudging someone from a higher economic class.
Then figure out how the theme you choose contributes to the work as a whole. How does it contribute to the conflict, structure, unity, etc.?