A plot diagram is shaped a lot like a triangle and shows the progression of a story line. It starts with setting, then moves through conflict and rising action. Climax is at the apex of the triangle. Then, coming back down the triangle we have the denouement and the resolution. While we cannot draw a diagram on this website, I can certainly review some of the major parts with you.
Setting: The book is primarily set in Hertfordshire, England, on the Longbourn estate.
Conflict: The two major conflicts are Character vs. Character and Character vs. Self. The conflict is introduced when we first meet Mr. Darcy. Elizabeth, our protagonist, thinks he is an arrogant prideful man and he insults her, but of course, as the story progresses, both characters have self-revelations.
Rising Action: The moment that Elizabeth chooses to stay at Netherfield with her ill sister is an important part of the rising action. It is here that we see Elizabeth engage in important conversations with Darcy that later prove to be ironic. It is also during these scenes that we first learn that Darcy is in danger of being strongly attracted to Elizabeth. Another important part of the rising action is when Elizabeth goes to visit Charlotte at Rosings Park. Here, Elizabeth also has important encounters with Darcy, leading up to the proposal.
Climax: The climax takes place the moment that Darcy first proposes to Elizabeth.
Denouement: The denouement, or "unwinding," or falling action takes place with respect to Elizabeth reading Darcy's letter of explanation. After reading this letter, Elizabeth begins to realize she has completely misjudged Mr. Darcy. She also realizes that she has been blind, vain, and has completely misjudged her abilities to discern. Likewise, Darcy begins to realize that though his pride was not out of place, he was very conceited.
Resolution: The resolution is that both Elizabeth and Darcy realize their character flaws and are happily united at the end. Jane is also happily united to Bingley. Also, Mr. Bennet realizes that he was at fault for the improper conduct of his family.