Short answers, pulled from the story.
Jón Árnason's 1862 collection Íslenzkar þjóðsögur og æfintýri contains the core folklore that shaped J. R. R. Tolkien's elves. Old English texts like Beowulf mention eotenas ond ylfe ond orcnéas, grouping giants and elves with demon-corpses. A Middle English source called South English Legendary from around 1250 describes elves dancing in secret paths by day and on high downs by night.
Tolkien developed his conception of elves over decades starting from early Victorian poetry influences. A production of J. M. Barrie's Peter Pan in Birmingham during 1910 influenced his later works alongside Catholic mystic poet Francis Thompson whom he acquired in 1914. His Book of Lost Tales written between 1917 and 1927 develops the theme that diminutive fairy-like Elves had once been great and mighty people who diminished themselves as Men took over the world.
The first Elves awakened near Cuiviénen bay during the Years of the Trees under starlit skies before Sun or Moon existed. Three pairs woke first: Imin and Iminyë Tata and Tatië Enel and Enelyë. They walked through forests finding other pairs who became their folk living by rivers while inventing poetry and music.
Tolkien created many languages for Elves primarily philological interest saying stories grew out languages indeed first thing ever created mythos starting called Elfin Qenya later spelled Quenya High-elven. Sindarin Grey-elven most complete Tolkien constructed languages alongside Quenya. Elves credited creating Tengwar scripts by Fëanor Cirth Daeron.
After One Ring destruction power Three Rings ended Fourth Age Age Men began most leaving Valinor. Those staying doomed slow decline until Galadriel words faded becoming rustic folk dell cave playing thousands years modern world occasional glimpses rustics fueling folktales fantasies. Legolas founded elf colony Ithilien during King Elessar reign helping rebuild Gondor living mainly southern Ithilien shores Anduin.