Who was Hestia?
Hestia doesn't appear in stories much. We have almost no images of her, either. She is one of the daughters of Rhea and Kronos, and so she is the sister of Hera and Demeter. And so of course Zeus, Poseidon, and Hades are Hestia's brothers. Hestia never marries and has no children.
Hestia is the goddess of the house, and especially of the hearth (fireplace) within the house, so she is the goddess of safety, security, doing your duty, taking care of things. Probably even though she is not in very many stories, she was actually a pretty important goddess, who was worshipped at home, as part of the ritual of lighting a fire or moving into a new house, or getting married.
D'aulaire's Book of Greek Myths, by Edgar and Ingri D'Aulaire.
Greek Religion, by Walter Burkert (reprinted 1987). By a leading expert. He has sections on each of the Greek gods, and discusses their deeper meanings, and their function in Greek society.