Most people meet the Theogony as a list. Who fathered whom, forty names in a row, and you start wondering when the story begins. I felt the same the first time through, and I skimmed. But if you stay with the lists long enough you notice they are doing a job. Hesiod isn't only writing down the gods. He is explaining why the world is run by the family that runs it, and why that should last.
A shepherd and some goddesses with a confession
Before any god appears, Hesiod puts himself in the poem. He says the Muses came to him on Mount Helicon while he was minding sheep. They called shepherds like him "mere bellies", which is not a warm greeting, and then they gave him a laurel staff and breathed a voice into him. Then they say something strange. They know how to tell many lies that sound like the truth, and, when they feel like it, how to sing what is true.
A poet opening his work by admitting that his source sometimes lies is a bold move. I read it as honesty. He is telling us this is a telling, and we should hold it loosely. That is also why this site says so at the bottom of every epic: a telling, not the only telling.
Before anybody has a name
Chaos comes first, and the word means a gap, a yawning space, not a mess. After it come Earth, then Tartarus deep underneath, then Eros. From Chaos come Erebus and Night, and those two have children of their own. Earth, on her own, produces Sky, the mountains and the sea.
Notice what is missing. Nobody makes the world. There is no workshop and no plan. First there is a separation, then there is reproduction, and soon the place is crowded. The Greeks who heard this did not have a creator to thank. They had a family to live with.
The sickle and the stone
Sky hated his children and pushed each one back into Earth as it was born. In pain, Earth made a jagged sickle and asked her sons for help. Only the youngest Titan, Cronus, agreed. He waited in ambush and cut his father down. Aphrodite came out of the foam that gathered round the severed parts, and Hesiod, who enjoys a pun, tells you her name comes from aphros, the Greek word for foam.
Cronus then took the throne and swallowed his own children, because he had been warned that one of them would overthrow him. When Rhea was expecting Zeus she hid him on Crete and handed her husband a stone wrapped in baby clothes. Hesiod says Zeus later set that stone up at Pytho, which is Delphi, as a marvel for mortals. Centuries on, Pausanias says he saw a stone there that people poured oil over every day and wrapped in wool at festivals. I like that the joke on Cronus ended up as a shrine.
Ten years and a hundred hands
The war that follows is the Titanomachy, and it drags on for ten years. It breaks open when Zeus frees the Hundred-Handers from their prison under the earth and feeds them nectar and ambrosia. They throw three hundred boulders at once. The Titans are buried under the earth and guarded by the very beings they had imprisoned. (There is a full piece on the war in the Myths section, so I won't retell all of it here.)
What I think the poem is really for
Here is my own reading. Twice in the poem a son takes the throne from his father. The question hanging over the whole thing is why it won't happen a third time. Hesiod's answer is that Zeus learned from the first two.
He shares out honors. He lets the old gods keep what they had and rewards the ones who fought for him. Styx came to his side first, and her children, Power, Force, Victory and Zeal, sit beside his throne for good. He marries Metis, whose name means cunning counsel, and when he learns her child could unseat him he swallows her whole, and Athena later comes out of his head. If you read that as a story about government, Zeus has absorbed advice itself. Nobody can plot against him from inside, because the plotting lives in him now. That is a very practical theory of power, and I think it is the point of the whole catalogue. This is our reading, not a settled one.
The hymn nobody expected
In the middle of all this, Hesiod stops for a long praise of Hecate. It has nothing to do with the plot. Zeus honors her above others, he says, and gives her a share of earth, sea and starry sky. She helps in assemblies, in battle, in athletic contests and with the herdsman's flocks, and she hears anyone who prays to her. Some scholars suspect the passage was added later. Others think Hesiod's own family worshipped her. Nobody knows. Either way, a goddess who barely appears in other early poetry gets a whole passage here, and that is why she belongs on a site like this one.
The first woman
Near the end of the gods' part comes Prometheus. At Mecone he tricks Zeus over the shares of an ox, hiding bones under shiny fat. Zeus takes the bones, hides fire from humankind in revenge, and Prometheus steals it back in a fennel stalk. Zeus answers with what Hesiod calls a beautiful evil, the first woman. He does not give her a name here. That comes in the next poem. Hesiod is not kind to women in this passage, and I'd rather say so than quietly excuse it.
If you want to read it
It is short, about a thousand lines, and you can read it in one sitting. M. L. West's translation in Oxford World's Classics has good notes. Skim the catalogues the first time. Then go back and see who is sitting next to whom.