J.R.R. Tolkien’s 1977 posthumous book about the creation of Arda and the history of the First Age is The Silmarillion.
The book opens with the Ainulindalë, a creation account describing the Music of the Ainur, and continues with the Valaquenta and the Quenta Silmarillion. These sections establish the divine powers, the world of Arda, and the wars and tragedies surrounding the Silmarils.
Its First Age narratives include the awakening of the Elves, Morgoth’s conflict with the peoples of Beleriand, and the stories of Beren and Lúthien and Túrin Turambar. The final sections move into later ages and explain the downfall of Númenor and the rings of power.
The Silmarillion was edited by Christopher Tolkien from his father’s papers. It is therefore a posthumous editorial construction rather than a manuscript completed for publication by J.R.R. Tolkien himself.