Short answers, pulled from the story.
Artemis is the daughter of Zeus and the Titaness Leto, and the twin sister of Apollo. The twins were born on the island of Delos after Hera, angered by Zeus's affair with Leto, forbade Leto from giving birth on solid land or any established island.
Artemis is the goddess of hunting, the wilderness, wild animals, transitions, nature, vegetation, childbirth, the care of children, and chastity. She was also worshipped as a patron of healing and a protector of young girls, and was one of the three major virgin goddesses alongside Athena and Hestia.
Actaeon was transformed into a deer and then killed by his own hunting dogs, who could no longer recognize their master. Different ancient sources give different reasons for his transgression, including accidentally seeing the goddess naked, boasting that he was a better hunter than her, or attempting to assault her.
The Temple of Artemis at Ephesus was located in the region of Ionia in what is now Turkey. It was counted among the Seven Wonders of the Ancient World. Of its 121 columns, only one composite column survives on the site today. At Ephesus, Artemis was worshipped primarily as a mother goddess rather than as a huntress, with priestesses called Melissa, meaning Bee.
Artemis demanded the sacrifice of Iphigenia, daughter of Agamemnon, as compensation for Agamemnon killing her sacred deer in a sacred grove and boasting that he hunted better than she did. When Iphigenia was brought to the altar at Aulis, Artemis took pity on her in most versions of the myth and substituted a deer, carrying Iphigenia away.
The Arkteia was a festival at the sanctuary of Artemis in Brauron, Attica, in which girls between five and ten years old dressed in saffron robes and acted as bears to appease Artemis. The ritual was linked to a myth in which the brothers of a girl killed a bear sacred to Artemis, and the goddess demanded that young girls "act the bear" at her sanctuary as atonement.