This is the simplest tool of all – Forster comes right out and tells us what people are like, and he even passes judgment in an overt and occasionally somewhat snippy manner. It's all just out there.
We learn a lot from the three family units we encounter – the Schlegels, the Wilcoxes, and the Basts. None of these are exactly conventional, and their unconventionality is what renders them so unique. The odd no-parent, all-kids set up of the Schlegels alerts us to a certain ambiguity of maturity in all of the siblings, while the Wilcoxes, who are dominated by their father (largely from a financial perspective) are almost too concerned with the adult world of business and money. Finally, the Basts' incomplete "family" demonstrates the utter dissatisfaction of their lives; their everyday behavior expresses nothing but frustration and lack.
Forster's third person narrator is comfortable moving in and out of the minds of his various characters, but he's more comfortable with some than others. We spend most of our interior time in Margaret's brain, through which we learn a lot about here, and also about the philosophical premises of the novel. The second most significant character we learn about through internal thoughts and opinions is Leonard Bast – the narrator's insight into his private world teaches us more than we could possibly figure out from his awkward, stunted exterior. We are also given the chance to visit Helen on occasion, and sometimes even minor characters like Tibby and Charles, though our views of how these characters work is more often than not simply validated by their inner workings.
The different modes of speech we encounter here, from Mr. Wilcox's brusque, somewhat condescending "man talk," to Leonard's awkward and halting conversation, to the endless flow of Schlegel babble all helps us understand the characters we encounter. Some, like Jacky, are hopelessly stunted; her language is repetitive and non-communicative (she mostly just says "What ho, Len!" and goes back to sleep), and is indicative of her low-level brain power. The Schlegels, however, constantly analyze and intellectualize everything, and therefore have to speak all the time – they can't help themselves. Speech can be viewed as a way into the characters' brain patterns, and "hearing" them talk is a clear way for us to view the ways in which they process life.
Education and culture are hugely important here, and not in any oblique fashion – Forster comes right out and sets up the conflict between the characters that care about culture, art, and education (the Schlegels) and those who don't (the Wilcoxes). In between is Leonard Bast, who cares deeply about these things, but doesn't have the funds to attain them. It's clear that education here is a marker for a certain kind of social class – the liberal class whose wealth is inherited, not the business-centric, cash-earning new money. Tibby is the clearest example of the depiction of education here; he is totally defined by his over-educated life, and academia is the be-all, end-all of his character.