This novel is about the culture clash between Native Americans and Americans. In the Native American worldview, magic, mysticism and the supernatural are part of their religion and their lives. When Tayo comes home from the war, he is severely damaged - he has PTSD and on top of that, already had psychological issues from his dysfunctional upbringing. As many of Silko's characters, though, Tayo is of mixed-blood, so part of him is steeped in Native American traditions and part of him is stepped in American life. White man's medicine is not working for him, so he tries to recover from his mental wounds using the traditional methods of the Laguna people. The Laguna medicine, however, also is inadequate for the new wounds of the 20th century.

If you read the information in the themes section at the link below, you can read about how witchery is important in this novel as a manifestation of evil in the Laguna culture. There is also a good discussion of the Laguna mythology and cosmology that will help you with your question.