Hel is a being before she is a place, and the sources move between the two without marking the change. She is Loki's daughter, thrown down by Odin to govern the dead who do not fall in battle, and she is described as half living flesh and half corpse. Whether Helheim is her hall, her whole realm, or simply where she is depends on the sentence.
The fullest account is Hermod's ride. When Baldr dies, Odin's son rides nine nights down and northward, crosses a bridge over the river Gjoll guarded by a woman who notes that he does not have the colour of a dead man, and finds Baldr seated in the hall. Hel agrees to release him if every thing in the world will weep for him. Everything does except one giantess, who is generally assumed to be Loki, and Baldr stays. It is the only bargain in the mythology that is refused on a technicality.
Snorri's descriptions of a hall with named furnishings and a shore of corpses for oath-breakers read very much like a Christian hell, and probably are. The older sense is plainer and grimmer: the dead go down, most of them, without judgement or torment, and the place is cold and it is not a punishment. That distinction is the same one Sheol carries in the Hebrew Bible.