I Know Why the Caged Bird Sings is the autobiography of Marguerite Johnson, better known as author Maya Angelou taking us through her life from her birth to the birth of her own son. Reader’s experience Angelou conveys the insecurities she felt as Marguerite and the love she felt for her family , as well as experiences in church and school. She also shares the terrifying event of being raped by a family friend, which resulted in his death and Marguerite turning mute for five years from the trauma of this event. She describes gaining friends and observing the problems brought about by class and caste systems of the South. From this point Marguerite moves to California and faces severe trials that end with her becoming pregnant, but making it through high school before delivering and taking full responsibility to the life she brings into the world. There is a very detailed summary at the link below.
Fortunately, such summaries are already widely available. There's a one page summary of Angelou's autobiography as part of the enotes study guide for the book, and you can also find more developed discussions of the book there.