These are the things that came either directly from the primordial chaos or one step removed from it. They form the basic elements of Greek cosmology. Putting these early things into categories is often difficult as they may simultaneously be a place, person, and/or state of existence. They require a rather elastic understanding. They are not a lot of references to explain them as most of the ancient writers concentrated on later periods.
Eros is love. Originally Eros was considered to have been one of the great forces spawned from the primordial chaos. In this role Eros causes the fury of procreation that brings into being the world as we recognize it.
In later myths Eros has been reduced to a pleasant but, minor god. By Roman times Eros has become Cupid. Quite a come down which continues to this day.
Night, and the goddess of the night. Nyx was spawned from the primordial chaos. After mating with Erebus she birthed the Upper Air (Aether) and Day (Hemera). On her own she gave birth to Doom (Moros), Death (Thanatos), Sleep (Hypnos), the Fates, and Nemesis. She lives in Tartarus and goes forth onto the world each day as Hemera returns to Tartarus. She successfully interposed with Zeus on Hypnos behalf to keep him from being barred from Mount Olympus.
At once both a place deep beneath even the underworld and a personification of the place. So dark and sunless is Tartarus that its gloom has its own personification - Erebus. To reach Tartarus an anvil dropped from the surface would fall for nine days. It is below the roots of the earth and the sea. Surrounded by a bronze fence with gates of iron it is used as the ultimate place of imprisonment. The Hecatoncheires a ct as its guards. Zeus imprisoned most of the Titans here.