Short answers, pulled from the story.
Norse mythology is the body of myths belonging to the North Germanic peoples, stemming from Old Norse religion. It survived through oral tradition and was written down primarily in 13th-century Iceland in texts including the Prose Edda and the Poetic Edda.
The most popular god among the Scandinavians during the Viking Age was Thor, the thunder god, whose hammer Mjölnir appears in archaeological finds from pagan burials. Odin, Freyja, Freyr, and Njörðr are also central figures, alongside lesser-mentioned gods such as Heimdallr, Týr, and Gefjon.
The Nine Worlds of Norse mythology surround the cosmological tree Yggdrasil. They include Asgard, where the gods live, and Midgard, the realm of humanity. Elves, dwarfs, jötnar, and other beings inhabit the remaining worlds.
Ragnarök is a foretold immense battle between the gods and their enemies in which the world is enveloped in flames. After the destruction, the world is reborn, the surviving gods meet again, and two humans named Líf and Lífþrasir repopulate the fertile new earth.
The Prose Edda was composed in the 13th century by Snorri Sturluson, an Icelandic scholar, lawspeaker, and historian. The Poetic Edda was compiled anonymously in the 13th century from earlier traditional material.
Norse mythology became a subject of scholarly study in the 17th century, when key texts attracted the attention of European intellectual circles. Scholars later used comparative mythology and historical linguistics to trace elements back to Proto-Indo-European mythology.