(Gen 4:9) And the YaHWeH said unto Cain, Where is Abel your brother? And he said, I know not: Am I my brother's keeper?(Gen 4:10) And he said, What have you done? the voice of your brother's blood cries unto me from the ground.(Gen 4:11) And now are you cursed from the earth, which has opened her mouth to receive your brother's blood from your hand;(Gen 4:12) When you till the ground, it shall not henceforth yield unto you her strength; a fugitive and a vagabond shall you be in the earth.(Gen 4:13) And Cain said unto the YaHWeH, My punishment is greater than I can bear.
Cain is given a stay of execution. According to Torah, a life for a life, especially in the case of murder. But, the Civil covenant for the nation Israel had not been written yet. Just and observation, the real point here is that we can see the self-centered Cain is not remorseful of his brother's death but only concerned about his own wellfare. And the merciful YaHWeH give Cain specail protection, a protection that Cain will put to good use.(Gen 4:14) Behold, you have driven me out this day from the face of the earth; and from your face shall I be hid; and I shall be a fugitive and a vagabond in the earth; and it shall come to pass, that every one that findeth me shall slay me.(Gen 4:15) And the YaHWeH said to him, "Therefore whosoever slayeth Cain, vengeance shall be taken on him sevenfold. And the YaHWeH set a mark upon Cain, lest any finding him should kill him.
We need to note that the land of Nod is "east" of the land of Eden and within this Eden territory was located the Garden -- the Garden of Eden. This land of Eden is where YaHWeH's presence was known to be, so all of the children of Adam and Eve were living in this special place, this land of Eden, from which Cain was forced to leave. Because Cain feared for his life, not from people in Eden, but for those living outside of the Eden territory. Perhaps the people of Nod saw the land of Eden as the land of the gods? Think about some of the ancient myths, the gods of the ancients all seem to be very human, with all the short coming and faults of humans but with godly powers, then they aways lived in a high place, like a mountain or in the clouds. Cain comes down from the moutain area of the gods and lives among the people of Nod, who, perhaps, see him as a god. This would not be the last time that humans would be worshiped as gods, our human history is full of Cains, with seemingly special protection.(Gen 4:16) And Cain went out from the presence of the YaHWeH, and lived in the land of Nod, on the east of Eden.
This is the first mention about Cain's wife. He could have married a sister but the context suggest he went to the land of Nod and there found a wife and started a family. However, Cain is not the only one to begin having children. After he left we are told about his parents, Adam and Eve, having more children, sons and daughters -- Genesis 5:4.(Gen 4:17) And Cain knew his wife; and she conceived, and bare Enoch: and he built a city, and called the name of the city, after the name of his son, Enoch.