What is in the first eleven chapters of Genesis?

They are written in poetry, which is a sign to the reader that they are metaphorical stories or contemplations rather than factual history. They are a kind of Hebrew mythology on "how the world came to be."

First they tell the story of how the world was created, how sin began and how the human race became worse and worse. Then it tells the story of Noah's flood - and how even this did not solve the problem of sin, because Noah's descendants continued sinning. Finally it tells of the Judgment of Babel: how the human race was condemned to misunderstand one another, and why only some people were going to be saved.