Theme and Structure
Book IV discusses the way in which Socrates approached important matters. I think that the point of this book is to give a more rounded picture of Socrates in action than Xenophon could give in the other books.
4.1-2 Xenophon first discusses how Socrates approached those who were proud of their education in general terms (4.1) and then gives a specific example through Socrates' discussion with Euthydemus (4.2).
4.3-7 We next get several sections discussing how Socrates focused on trying to develop sophrosyne, sober judgment, in people by encouraging reasonable piety (4.3), taught them justice by showing what it was in his actions (4.4), helped them to be more competent in their tasks through philosophical dialectic (4.5), helped them to be better at philosophical dialectic itself (4.6), and assisted them in becoming self-sufficient (4.7).
4.8 We then end the book and the work with a brief discussion of the meaning of Socrates' death.
Euthydemus probably is being used by Xenophon as a typical student, but he is also mentioned in Plato's Symposium. We get a lot of similarities between Xenophon and Plato in these sections. We also get the discussion with Hippias of Elis in 4.4, and the portrayal of the interaction is in many ways very similar to the portrayal we get in Plato's Hippias Major and Hippias Minor. But the most notable point is the discussion with Hermogenes (4.8), who was Xenophon's source for the events of Socrates' last days (Xenophon himself was was not in Athens at that time, off in Persia and then Sparta, experiencing the events that he would write up in the Anabasis).
Hermogenes, after Meletus had laid his indictment, heard that Socrates was discussing things other than his trial, and told him that he should work on his defense. In response to this, Socrates asked, "Don't you think my whole life has been a preparation for it?" -- namely, by devoting his life to the study of right and wrong. When Hermogenes responds that juries have been known to condemn innocent men, he responds that his daimonion prevented him from working on it. But Socrates remarks that up to that point in his life, he had as pleasant and good life as could be wished; his death will spare him the slow loss of that. Further, he knows how reputation works; if unjust men put him to death, it will still be known that he always tried to make his associates better people.
Quotations from Robin Waterfield's revised translation of Hugh Tredennick's translation in Xenophon, Conversations of Socrates, Tredennick & Waterfield, trs. Penguin (New York: 1990).