Conversations play a huge role! Austen is the queen of detailed, elaborate, flowery, lengthy conversations between characters. This is why many people struggle with her novels, and why others love them. A conversation can start on one page and ten pages later still be going. Consider Austen's background and life herself; living in England in a time when women were expected to sit around and do practically nothing all day, what else did they have to do besides talk?
Conversations help relay crucial and important information, shape the characters in the novel, introduce conflict, and resolve problems. One major role it plays is in shaping the characters of the story. Austen always has a garrulous and excessively chatty character that says foolish things and is a bore and annoyance to everyone around them (Mr. Collins, as an example). She likes to use conversation to shape those types of characters. Her heroines (like Elizabeth or Jane) are often more limited and wise in their conversations, being the listeners as opposed to the spouters.
Consider also how much of the NON-conversation narration in the novels centers and focuses around conversations that were just had. The characters not only have long conversations, but then go home and sit there and analyze every tiny thing that was said in that conversation for potential hidden meaning. So even though they aren't talking constantly, most of the story IS centered round people talking OR analyzing the talking that has occurred. It reminds me of a group of teenage girls talking about a party that a cute boy talked to them at, and they all analyze and interpret, and read meaning into each and every word that poor boy said. That is what the characters do.
So, whether is it actual talking to shape characters, introduce conflict or resolve it, or if it is the characters thinking about what was just said, conversation is the main driving force in Pride and Prejudice. I hope that helped; good luck!