Genesis 4: 16 - 26

¹⁶And Cain went out from the presence of the LORD, and dwelt in the land of Nod, on the east of Eden.  ¹⁷And Cain knew his wife; and she conceived, and bare Enoch: and he builded a city, and called the name of the city, after the name of his son, Enoch.
 ¹⁸And unto Enoch was born Irad: and Irad begat Mehujael: and Mehujael begat Methusael: and Methusael begat Lamech.
 ¹⁹And Lamech took unto him two wives: the name of the one was Adah, and the name of the other Zillah.
 ²⁰And Adah bare Jabal: he was the father of such as dwell in tents, and of such as have cattle.
 ²¹And his brother's name was Jubal: he was the father of all such as handle the harp and organ.
 ²²And Zillah, she also bare Tubalcain, an instructer of every artificer in brass and iron: and the sister of Tubalcain was Naamah.
 ²³And Lamech said unto his wives, Adah and Zillah, Hear my voice; ye wives of Lamech, hearken unto my speech: for I have slain a man to my wounding, and a young man to my hurt.
 ²⁴If Cain shall be avenged sevenfold, truly Lamech seventy and sevenfold.
 ²⁵And Adam knew his wife again; and she bare a son, and called his name Seth: For God, said she, hath appointed me another seed instead of Abel, whom Cain slew.
 ²⁶And to Seth, to him also there was born a son; and he called his name Enos: then began men to call upon the name of the LORD.

So, Cain has killed his brother, he is told to leave and is given a mark so that none will harm him. Cain leaves, has a wife and has a child. We are only in the fourth chapter and once again we are confronted by the question of who else was on the earth. Either Adam and Eve had other children before or at the same time as Cain and Abel (and we have no evidence of that whatsoever), Cain slept with Eve (and we have no evidence of that) or there were in fact other people (and that is what we discussed when talking about Genesis 1 and 2.

We are told about some of Cain's children and how Cain built a city and named it after his son. Cain did not name the city after himself, that sort of implies he was proud to be a father. One of the descendents of Cain was Lamech and he seems to be a pretty vain person. He says that anyone who hurt Cain would have harm returned to him 7 times more and he says that anyone who hurts him will have harm returned to him 77 times more. We are not told that God said this, only that Lamech said it.

Adam and Eve have a couple of more children and that is when people begin to talk about the Lord. That is sort of interesting, it means that Cain was not talking about the Lord to the people he was around. Maybe he didn't want to discuss what had happened to him and how the Lord had separated Cain from himself.