This chapter is about people makin' babies. Looks like everyone's obeying God's command to "be fruitful and multiply" (1:28).
The narrator starts by summarizing the creation of humankind. The summary is consistent in language with the first creation story (compare 1:26-28), and we are also back to God (Hebrew: 'elohim) as the name for the deity as in 1:1-2:4.
The genealogy is pretty formulaic and repetitive. The basic recurrent elements include: (1) how long each figure lives before bearing a son; (2) the name of the son; (3) how long each figure lives after bearing a son; (3) the fact of their death; (4) the total number of years for their life. Ta da!
These pre-flood figures are notably very old when they die. They usually fall just short of one thousand years.
Yep, that's 1,000 years.
FYI, there's no textual indication that years are being counted differently than normal. The bare fact is that these figures of the primordial age had a much longer lifespan than subsequent characters in the story do. Maybe we should be thinking of these guys as semi-divine, larger-than-life heroes of old.
Departures from the typical genealogical formulas are very significant, and we get two of them.
The first has to do with Enoch: "Enoch walked with God; then he was no more, because God took him" (5:24 NRSV). Hmmm, where did God take him?
In later Jewish literature, Enoch returns and reveals all the secrets of heaven and the future. Nifty.
The second departure from genealogical formula is with Noah, whose name sounds like the Hebrew word for "console" (nahem). Noah's is five hundred years old when he begets Shem, Ham, and Japheth.