Short answers, pulled from the story.
The name Iphigenia means strong-born or born to strength. Ancient lexicons define it as she who causes the birth of strong offspring. Scholar Karl Kerenyi suggests a deeper meaning when he renders her name as she who governs births mightily.
Agamemnon sacrificed his daughter Iphigenia because Artemis prevented the allied troops from reaching Troy through her control of the winds after he killed one of her sacred stags. Calchas the seer told Agamemnon that appeasement required him to sacrifice his eldest daughter, Iphigenia. The goddess accepted a full-grown deer in place of the child and snatched Iphigenia away to make her immortal.
Artemis transported Iphigenia to the Tauroi making her immortal where she became the priestess of Artemis at her temple in Tauris which was known as Crimea in antiquity. Later Athena sent Iphigenia to the sanctuary of Artemis at Brauron where she served as priestess until death. Some sources claim Artemis left a goat actually the god Pan in her stead instead.
Orestes arrived at Tauris with Pylades son of Strophius and they were immediately captured by the Taurians who had a custom of sacrificing all Greek strangers to Artemis. Iphigenia recognized her brother when Orestes revealed his identity and they escaped together carrying the image of Artemis back to Greece. Athena guided them safely through dangers along the way back to Greece.
Euripides wrote two plays about her fate: Iphigenia at Aulis and Iphigenia in Tauris set in the Heroic Age during the fifth century BC. Homer does not explicitly mention the sacrifice although scholars argue it lies allusively behind opening scenes of the Iliad. Lucretius used the story as criticism of religion in his poem De rerum natura while Ovid retold the myth in books twelve and thirteen of his Metamorphoses narrative poem.