The hardest part of the novel to understand is probably the Prologue. How does a Dick and Jane reader relate to the events in the novel? Morrison seems to want to juxtapose popular depictions of so-called normal family life with other kinds of families that aren't so peachy (or monosyllabic).
Morrison switches up the narrative style sometimes, too. So while some chapters feature mostly Claudia narrating, others have funky things like Pauline telling her story in first person, or Pecola and her imaginary friend speaking in dialogue.
In the Afterword, Morrison says she wanted to avoid demonizing either Pecola or her community, and this is why she chose to use multiple perspectives in the novel. So rather than frustrating us, we might think about how these shifts in perspective shake things up, make the reading more interesting, and help us get into the psyches of some of these complex characters.