It begins with Adam and Eve having sex, an activity which produces two sons, Cain and Abel.
Abel becomes a livestock farmer and Cain decides to spend his time in the arable business. For some reason which isn't made clear, God comes down and judges the merits of their produce.
God decides he prefers the animals, making Cain rather jealous. So jealous in fact, that he murders his brother.
Again, God doesn't know whodunnit, but he teases a confession from Cain whom he subsequently condemns to the life of a tramp. Cain protests that he'll be killed in retribution (by whom? Adam and Eve?) but God offers him protection, saying that he'll visit sevenfold punishment on anyone who makes an attempt on Cain's life.
With this immunity, Cain goes to the "Land of Nod" and begins a dynasty and builds a city (does God never stick to his word? Cain's supposed to be a tramp, Adam and Eve were supposed to die the day they ate from the magic tree....walk it like you talk it Lord).
There are plot holes here that a five year old could spot. Adam and Eve clearly weren't the only people on Earth as Cain, in exile, is able to find a wife and father children with apparent ease. Go figure.
And so the chapter ends as it began: Adam and Eve get down to business and produce another boy, who they name Seth.
Chapter five is rather dull. I'd skip it if I were you. It's a yawnworthy account of the descendents of Adam up until Noah and his sons, there's a whole lot of begetting and not much else. Snore.