Which Tolkien work presents the creation of the world and the First Age legends of Middle-earth?

The Silmarillion presents the creation of the world and the First Age legends of Middle-earth.

The book opens with the Ainulindalë, a creation account describing how Eru Ilúvatar and the Ainur bring the music and design of the world into being. It then follows the shaping of Arda, the arrival of the Valar, and the history of the Elves and other peoples across the earliest ages.

Its central narrative, the Quenta Silmarillion, concerns the three Silmarils made by Fëanor. The jewels are stolen by Morgoth, the first Dark Lord, and the resulting oath of Fëanor drives much of the tragic history of the First Age. Stories include Beren and Lúthien, Túrin Turambar, and the fall of Gondolin.

The Silmarillion was edited and published posthumously by Christopher Tolkien in 1977. It is not a conventional single novel, but a collection of connected mythic histories, chronicles, genealogies, and texts representing Tolkien’s extensive invented tradition.