“Book” in verse 1 is the Hebrew word sefer which means a written record. This is additional evidence from the beginning that Genesis is not an orally transmitted (i.e., evolved) mythology of the Hebrew people, but beginning with Adam, this history was written down.
As Adam was God’s son, so Seth was Adam’s son. From the very beginning of Genesis God is revealing who He is to man: Creator, then Judge, but just as importantly, Father.
The son whom Adam begot, was Seth. No mention is made of Cain or Abel. This is because Abel was dead and could not bear children to continue Adam’s line, and Cain, although alive and bearing children, was shown, in the last parashah, to be fathering a line of children who did not know the presence of God and who followed in their father’s footsteps in doing evil. Thus, by following the geneaology through Seth in this parashah, Torah is making a distinction between two families of men in the earth: the family of Cain, the unrighteous seed who rebelled, and the family of Seth, the righteous seed who obeyed.
This is a sixth teaching tool of Torah: comparison, and contrast. God places two different geneaologies next to each other, why? So that we can discover, by comparing them, how they are similar or different.
Then we discover that after bearing other sons and daughters (Josephus states that Adam bore thirty-three sons and twenty-three daughters), Adam died, after 930 years. God promised him that if he ate the fruit, he would die, and so he did.
The topic of the parsha stumah from Gen 5:1-5 is the mortality of Adam.