A character sketch is a brief description of a character. The word "sketch" should make you think of art, where an artist rapidly creates a design. It doesn't have to include many details, and it isn't necessarily finished.
Some of the main characteristics of Anne Frank include her outgoing and talkative nature. Peter provides an example of this when he explains,
"All right, Mrs. Quack Quack! . . . I heard about you...How you talked so much in class they called you Mrs. Quack Quack! How Mr. Smitter made you write a composition, "'Quack, quack' said Mrs. Quack Quack."
Anne was known for being very verbal and talkative around her school. Additionally, Anne cares deeply for her family and friends. This is seen when she goes out of her way to find and create presents, when she and her family have hardly any money or resources, for the members of the secret annex. She loves people and enjoys conversing with them. Finally, Anne also has a very optimistic view of the world. She famously wrote in her diary,
"In spite of everything, I still believe that people are really good at heart."
Peter, however, enjoys his peace and quiet. Throughout much of the dramatic version of The Diary of Anne Frank, Peter tries to be by himself in his room. After he tells the others about how Anne was called Mrs. Quack Quack in school, the two of them continue to bicker. Finally, he exits:
"Quack, quack, quack, and from now on stay out of my room!"
Peter liked his alone time, especially with his cat, Mouschi. In fact, Peter seems to be a bit like his cat. As he explains to Anne when she tries to be friendly with Peter's cat,
"He's a tom. He doesn't like strangers."
Later, when Anne and Peter become friends, he tells Anne directly that he didn't believe he had any friends:
"I don't want any [friends]." I get along all right without them."
However, by the end of Anne's diary (and the dramatic version), Peter learns to consider Anne a true friend. In the play Anne asks Peter if he could, "get along without [her]?" He responds,
"No. If they were all like you, it'd be different."
Peter is much less interested in socializing than Anne is. He's also less talented in academics than Anne and her sister, Margot. Finally, Peter is much more pessimistic than Anne. One example of this is when Peter tells Anne that he doesn't have (or need) any friends.