The Meryton Assembly Ball takes place in Ch.3. What happened during that ball is discussed in the next two chapters
Charles Bingley: In Ch.3 we read that "Mr.Bingley was good looking and gentlemanlike; he had a pleasant countenance, and easy unaffected manners...He was lively and unreserved." Bingley is immediately attracted to Jane and expresses her admiration for her by dancing twice with her. In Ch.5 Charlotte remarks that she heard Bingley telling Mr.Robinson that he thought that Jane was the prettiest of all the young women at the ball.
Darcy: In Ch. 3 at the ball, "the ladies declared he was much handsomer than Mr.Bingley," but he had "a most forbidding, disagreeable countenace." And although he was the owner of a large estate in Derbyshire and his annual income was ten thousand pounds a year everyone found his proud behaviour disgusting. He refused to be introduced to anyone at the ball and danced only with the Bingley sisters. Worse, he insulted Elizabeth by refusing to dance with her by remarking, "she is tolerable, but not handsome enough to tempt me."
The Bingley sisters: In Ch4. we learn from Elizabeth's observation that although they were good looking "their behaviour at the assembly had not been calculated to please in general." They were well provided for, had had a good education, but were extravagant, "proud and conceited" and "thought well of themselves and meanly of others."
The major themes are shown through the actions of the Bingley party. While Charles Bingley is inclined to thinking favorably of the Bennets and their small country town, the others are not. Darcy and the Bingley sisters are proud of who they are and of their background. This pride makes them prejudice against anyone not of their station in life. This pride and prejudice can be keenly felt as you read about their visit to Netherfield.
They spend all their time in the country making fun of the people in the town, most especially the Bennet family, because the country way of life is different from their own. The way they speak and behave is seen as being less dignified and polite than the Bingley party. It is also revealed that the Bennets' lack of money is a big setback for them marrying into a good family. Darcy and Bingley's sisters often comment on how Jane seems to be so much above her station (meaning that she has better manners and seems more educated than those around her), but the fact that she is poor should keep Charles from being interested in her. The fact that this does not keep Charles from liking her shows that he is much less proud than this friends.