Unable to get dating advice from his sister, Charlie gets some from Sam. Some advice, we mean—although he really wants something else from her.
Charlie's a little upset that Sam isn't jealous of Mary Elizabeth. Instead, she tells him to tell Mary Elizabeth that her outfit is nice, not that she looks pretty. "Her outfit is her choice whereas her face isn't" (3.6.4). Hmmm, interesting point.
Other advice? Ask a lot of questions and listen to the answers, even if she talks a really long time. Oh, and he should kiss her the same way she kisses him.
Charlie tries to get a practice kiss from Sam, but she shoots him down. Even though his move doesn't succeed, it's actually a rare suave moment for our little narrator.
At the end of the letter, Charlie tells us that he wishes he could stop loving Sam. But he can't.