As soon as *he left the Garden of Eden for good*, Adam lay with Eve who conceived. To make a baby just after being expelled from their home with yet no place to go, was an act of impetuosity, which caused Eve much guilt. So she tried to put the best face on what she’d done, and said to God, “With the help of the Lord I have brought a man into being”.
It was wounding for Adam to hear this, for Eve was, in effect, impugning his masculinity by saying that she’d needed help from another man (God) to bring the child into being. Eve, in addition to feeling guilty about her co-irresponsibility, was also resentful of Adam for putting her in this position.
The child, a boy, that Eve bore was called Cain. Afterwards, she (Eve) had another son, who was called Abel.
Abel became a shepherd, and Cain a tiller of the soil. One day Cain presented to God some of the food he’d grown. Not to feel outdone, Abel presented God with the first-born of the sheep that he shepherded. God received Cain’s sheep with gratitude. He refused, however, the food from Cain. Cain was very angry and his face fell. God, seeing this, explained that He felt that Cain hadn’t done well enough, and that he could do better.
Cain said to Abel, “Let us go into the open country”. While there, Cain slew Abel. When Cain returned from the country, God, noting the absence of Abel, asked Cain where Abel was. Cain said he didn’t know, and petulantly added, “Am I my brother’s keeper?”
God said to Cain, “What have you done? The voice of your brother is crying unto me from the ground. You are henceforth cursed from the earth which has opened her mouth to receive your brother’s blood from your hand. When you till the ground, it will no longer yield you its wealth. You shall be a fugitive and a vagabond on earth.”
“My punishment is greater than I can bear” said Cain. “You are driving me from the earth, so that I must hide myself from You. I’m condemned to be a fugitive and vagabond. Everyone who sees me will want to kill me. This isn’t fair”.
However, God said to Cain, “No, if anyone kills you, you shall be avenged sevenfold.” Accordingly, God put a mark on Cain, so that anyone seeing him would know not to kill him. Cain then went away and settled in the land of Nod, to the east of Eden.
When in Nod, Cain found himself a wife and lay with her. She conceived and bore Enoch. Meanwhile, Cain was building a city which he named Enoch, after his son.
But, what had become of Cain’s father and mother, Adam and Eve, who had been so cruelly deprived of their younger son, Abel, because of what Cain had done? Well, Adam lay again with Eve, who bore a son whom she named Seth. Seth was Abel’s replacement. Eve said as much, for she said, “God has granted me another son in place of Abel, because Cain killed him”.
Seth, who was Cain’s new brother, later on had a son, whom he called Enosh, who was therefore the cousin of Enoch, Cain’s son.
Source: Genesis 4