Historically, the book has been attributed to Moses, but current scholarship does not, leaving the author of this book unknown. It is likely to be a compilation of several authors. (Comparing chapter 1 with chapter 2 and 3, we see a different emphasis and order to creation which could well come from different authors.).
The stories in this book begin with creation itself and follow through the lives of the patriarchs until Joeseph's death after his family is settled in Egypt. The stories themselves are from before Israel existed as a nation or even as tribes but only as a family. As such these stories are likely to have been passed down through the generations in oral tradition.
The book itself did not exist in its present form until the exile in Babylon. This is important because there is a marked contrast in the ways that Babylonian creation stories and Hebrew creation stories view the act of creation, the world, and human beings.
Most of the places referred to in Genesis are in or around the eventual land that comprised the kingdom of Israel. In the early chapters, other cities throughout the ancient Middle East are named. Egypt also figures in a number of stories.
The stories revolve around the family tree that eventually brings Abraham and Sarah, Isaac and Rebeccah, and Jacob, whose name becomes Israel and Rachael. Many of the stories revolve around difficulties in having children and thus continuing the family line.
The stories also follow the promises of God to these people. The purposes seem to be to show that God's promises are given and kept, often regardless of the worthiness of the people receiving them. The stories also show how human beings work to understand God and how God works in their world.