Although this book is easy to read, you might get kind of confused about some of the culture and history. Here are a couple of things to know that might help you:
Bride-price: Bride-price is a marriage custom common among many African ethnic groups, but is definitely part of the Igbo people's traditions. Bride-price is not "buying a bride," though many Americans mistakenly define it that way. Bride-price is an agreement between families, the groom's family and the bride's family. It transfers the bride's reproductive powers over to the groom's family. So essentially, the groom's family is paying the bride's family so that they can lay claim to the children that the bride bears. Otherwise, the children belong to her family.
You might wonder why this is important. For centuries, Africans in many countries survived in the tropics because of heavy labor. In order to clear the tropical forests for a home and for farming, in order to grow sufficient amounts of food, Africans needed access to lots and lots of labor. This meant that having people around was extremely important for survival. The more people you had, the more access to labor you had. In other words, the more people you had, the wealthier you were. One way people got this labor was through slavery. But another way was to have children.
So when a family released their young daughter to another family, they were not only losing her labor but her children's labor too. The groom's family compensated the bride's family for their loss by paying them a hefty price of cattle. Interesting side note: in stark contrast to the idea of "buying a bride," the bride-price made it actually much easier for a woman to divorce her husband and take her children with her. All she needed to do was convince her father to give back the bride-price cattle, and she could leave and take her children with her.Chi: A man or woman's chi is their personal god. Their chi may give a person good luck or their chi may give a person bad luck, but as Joseph pointed out, you never want to challenge your chi because it could turn against you. The Igbo understand three levels of deities: the creator god, minor deities that use varying levels and different types of spiritual power, and of course, the chi.
Osu: An osu is a living sacrifice to a god. They and their children are untouchable and, for the most part, considered to be slaves. A non-osu may get contaminated by associating with an osu. A bill introduced to the Nigerian government in 1956 called for the abolishment of the system, suggesting it as similar to apartheid as practiced in South Africa (source).