One quick note on the Greek text. I got if from Perseus Tuffts The text there is identical to the one in the Loeb Library edition, Hesiod, The Homeric Hymns, and Homerica by Evalynn G White. The passage follows the description of Zeus defeating the Titans and giants in a battle for who would rule heaven and earth and hell.
A couple opening observations: Tartarus is below the earth as the sky is above. One must imagine a flat earth of a certain thickness. The bronze fence and the strings or lines of night is a bit confusing to me, but it is obvious that from the underworld you look up at the roots of things (trees?) hanging down from the roof which is earth far above. Also, one is looking at the bottom of the sea. The epithet of the sea ἀτρυγέτοιο is interesting. “Unharvested”, “barren”, literally an appositive and fruitful so “fruitless.” It is a fairly comment descriptor of the sea, but what is it supposed to mean. Unharvested is perhaps the most positive possibility, but I think it is supposed to suggest the vast expanse of sea in which one sees only swells and the horizon.
Gyes, Cottus and Obriaros are Titans who sided with Zues and who guard the other Titans imprisoned in Tartarus.Lots of repitions of dank and damp and dark in various forms.
The son or Iapetus is Atlas, who holds up the earth and sky.
Sleep and Death are the children of Night.
The "terrible dog," one would presume is Cerebus, though he does not yet have his three heads.
Styx is a river and also a goddess of Tartarus. The gods would swear by her waters when they wanted or were required to make an unbreakable oath. The consequences of breaking such an oath are spelled out in the next few lines.