The repetitive use of the word תולדות toledot (King James Version: "generations") seems to be a key to understand the structure of Genesis and the development of thought within the book:
With the exception of 1:1 the rest of what you could view as main sections begins with a toledot formula:
1. 1:1 In the beginning God created the heavens and the earth. 1:1 - 2:3
2. 2:4 These are the toledot of the heavens and the earth. 2:4 - 4:26
3. 5:1 This is the book of the toledot of Adam. 5:1 - 6:8
4. 6:9 These are the toledot of Noah. 6:9 - 9:29
5. 10:1 And these are the toledot of the sons of Noah. 10:1-11:9
6. 11:10 These are the toledot of Shem. 11:10-26
7. 11:27 And these are the toledot of Terah. 11:27-25:11
8. 25:12 And these are the toledot of Ishmael. 25:12-18
9. 25:19 And these are the toledot of Isaak. 25:19-35:29
10. 36:1 And these are the toledot of Esau 36:1-8
(inclusion: Esau who is Edom).
11. 36:9 And these are the toledot of Esau 36:9-37:1
(inclusion: Esau the father of Edom).
12. 37:2 These are the toledot of Jacob. 37:2-50:26
1. In the first section God creates the heavens and the earth. The creation of man (male and female) is only part of this bigger picture, even though as the peak of creation they were being created in God's image.
2. The second section tells us what has come out of the heavens and the earth (the toledot of the heavens and the earth: toledot meaning what is "born" or what has been "generated" out of the heavens and the earth). It is not a second creation story, but tells us, what comes out of heaven and earth: Adam and Eve come out. Adam coming out of the earth (2:7), and Eve out of him. Here the emphasis is narrowed down to the paradise garden and Adam and Eve, because their sin and the aftermath will change the earth, bring the curse to the earth (Gen 3:17) and curse on part of mankind (4:11).
3. The third section presupposes that Adam (and Eve) are already introduced and now dwells on what comes out of Adam (toledot of Adam). It is not his story, but what has come out of him, meaning the line from him to Noah, whose toledot will be the next.
4. The toledot of Noah describes what has come out of him and with him: His children and the animals saved through his arch, the new covenant of God with all of mankind, meaning all the descendants of Noah. The new world would have been unthinkable without what has come out of Noah.
5. The toledot of the sons of Noah describe what has come out of the sons of Noah: all the different nations of the world.
6. The toledot of Shem tell us what has come out of Shem, especially the chosen line from Shem to the family of Terah, whose will be the next and the seventh toledot.
7. The toledot of Terah do not tell his story, but what has come out of him, namely his children, especially God's chosen one Abram. This immense toledot (11:27-25:11) is not by chance the seventh section: Here the chapters 1-11 come to a closure which have told the general story of creation and revelation of God with regard to all nations and now God opens up the special revelation history with creating one special people the descendants of Abram. It is Abram's story, but the title is still: The toledot of Terah.
8. The toledot of Ishmael, which is a short section (25:12-18), tell us, what has come out of Ishmael, namely his descendants. In the way of Genesis the line which is not chosen is handled first and brought to a closure and then comes the chosen line.
9. The toledot of Isaak (a long section: 25:19-35:29) describe what has come out of him, namely his children, especially his son Jacob. In a way we could say the this section is the story of Jacob, but the title still is "toledot of Isaak", Jacob has come out of his father.
10 and 11: Esau has two toledot sections. Again the line which is not the chosen one is handled first and brought to a closure. But it is special that Esau gets a double toledot section. Why is that? I think the first toledot, the toledot of Esau in 36:1-8 with the inclusion: "Esau who is Edom" puts an emphasis on Esau as the beginner of the people Edom, an emphasis on his descendants. The second toledot, the toledot of Esau in 36:9-37:1 with the inclusion: Esau the father of Edom, puts an emphasis on Esau as the origin of a certain political structure and kingdom on mount Seir. 36:31 is important for this understanding: "And these are the kings that reigned in the land of Edom, before there reigned any king over the children of Israel." I understand that 37:1: "And Jacob dwelt in the land wherein his father was a stranger, in the land of Canaan" still belongs to this Esau toledot putting a contrast between the chosen one Jacob, who still lived in Canaan because of God's promise as a powerless stranger, while his brother whose toledot we are just reading had rapidly developed into part of a powerful local nation with kings even before God would give Israel a king (see the promise in Gen 17:6). For the more worldy beholder Esau was more blessed than Jacob who still had a long way to go (rest of Genesis until book of Joshua) until he would inherit his promised land.
12. The last toledot section of Genesis, the toledot of Jacob will actually tell us the story of mainly Joseph and his brothers, especially Judah (see Gen 38 and Judah's role in Gen 44 and the fact that Joseph and Judah get the main emphasis in the blessings in Gen 49). It is again what has come out of Jacob what is the content of this toledot of Jacob.
Just to say it again for emphasis: According to this toledot structure of the whole book of Genesis the vers in Gen 2:4 does not start a second creation account but tells us what has come out of heavens and earth, which had been already created in the first section (1:1 to 2:3). The first section could not have started with a toledot section, because there was nothing from where anything could have come out of. In the first section God had to set the beginning by creating the heavens and the earth. Then there was something where something could come out of.