sons of God marrying the daughters of men

what is the meaning of genesis chapter 6 ? who were the sons of God ? what is the truth and meaning to be derived from the story of Noahs flood ? what is the truth of Noahs flood and who were the sons of God ? did angles and humans Procreate in Genesis chapter 6 ? Does The Bible teach that angels can procreate with humans ? Who were the sons of God and the daughters of men in Genesis chapter 6 ? What does The Bible say about pre flood, stone age history of mankind ?