Tools of Characterization
Much of what we learn about the characters we learn through what they do. For example, Eva quite possibly "loses" her leg in a train accident because she needs money to support her kids. This tells us how tough a woman she is and that she's willing to do whatever it takes to survive. When Shadrack marches up and down the street in honor of National Suicide Day, we learn that he's been traumatized by war and that his fragile psyche needs a way to deal with death.
Morrison reveals a lot about the characters by simply telling us about them. Take a look at this passage about Sula and Nel: "It was in that summer, the summer of their twelfth year, the summer of beautiful black boys, that they became skittish, frightened, and bold – all at the same time" (1922.24). We don't have to see the girls do anything specific to know about their fear and boldness; it's enough for Morrison to simply tell us that it's there.
As we discuss elsewhere, Nel's family life is as unsatisfying as Sula's, and in some pretty similar ways. Both have mothers who tolerate them but never show any real love, both fathers are out of the picture, and both want something different than what they have. What does this tell us about their characters? That they have unfulfilled needs, that they recognize something in the outside world that is more promising than what they have at home, and that the many things they lack from their family they try to fulfill for each other. Family life helps us understand what drives the girls' hopes and dreams.
Characters' names are of great significance in this novel; they are often direct reflections of the characters and their personalities. Sula's last name is Peace, which might be ironic, since she brings anything but peace to the people in her life. Nel's last name is Wright. That's close to "right," and Nel is the character who always does the right thing, what's expected of her.
Sex and Love
Hannah and Sula's (and even Eva's) attitudes toward sex tell us much about the women they are. Sex is a vital part of their lives because they love the idea of men and masculinity. While most of the townspeople regard them as trampy, they don't seem to mean any harm by sleeping with married men. They simply regard sex as routine, and they see no harm in fulfilling their desires.