First Age follows Years of the Trees
In J. R. R. Tolkien's legendarium, the history of Arda, also called the history of Middle-earth, began when the Ainur entered Arda, following the creation events in the Ainulindalë and long ages of labour throughout Eä, the fictional universe. Time from that point was measured using Valian Years, though the subsequent history of Arda was divided into three time periods using different years, known as the Years of the Lamps, the Years of the Trees and the Years of the Sun. A separate, overlapping chronology divides the history into 'Ages of the Children of Ilúvatar'. The first such Age began with the Awakening of the Elves during the Years of the Trees and continued for the first six centuries of the Years of the Sun. All the subsequent Ages took place during the Years of the Sun. Most Middle-earth stories take place in the first three Ages of the Children of Ilúvatar.
Major themes of the history are the divine creation of the world, followed by the splintering of the created light as different wills come into conflict. Scholars have noted the biblical echoes of God, Satan, and the fall of man here, rooted in Tolkien's own Christian faith. Arda is, as critics have noted, "our own green and solid Earth at some quite remote epoch in the past." As such, it has not only an immediate story but a history, and the whole thing is an "imagined prehistory" of the Earth as it is now.Ages of the Children of Ilúvatar
The First Age of the Children of Ilúvatar, or Eruhíni, began during the Years of the Trees when the Elves awoke in Cuiviénen in the middle-east of Middle-earth. This marked the start of the years when the Children of Ilúvatar were active in Middle-earth.First Age
The First Age of the Children of Ilúvatar, also referred to as the Elder Days in The Lord of the Rings, began during the Years of the Trees when the Elves awoke at Cuiviénen, and hence the events mentioned above under Years of the Trees overlap with the beginning of the First Age.Having crossed into Middle-earth, Fëanor was soon lost in an attack on Morgoth's Balrogs – but his sons survived and founded realms, as did the followers of his half-brother Fingolfin, who reached Beleriand after Fëanor's death. In the Dagor Aglareb or Glorious Battle, the armies of the Noldor led by Fingolfin and Maedhros attacked from the east and west, destroying the invading Orcs and laid siege to Morgoth's stronghold Angband. The Noldor for a time maintained the Siege of Angband, resulting in the Long Peace. This Peace lasted hundreds of years, during which time Men arrived over the Blue Mountains. Morgoth broke the siege in the Dagor Bragollach, or the Battle of Sudden Flame. 
The Eldar, Edain and the Dwarves were all disastrously defeated in the Nírnaeth Arnoediad or Battle of Unnumbered Tears, and one by one, the kingdoms fell, even the hidden ones of Doriath and Gondolin.At the end of the age, all that remained of free Elves and Men in Beleriand was a settlement at the mouth of the River Sirion and another on the Isle of Balar. Eärendil possessed the Silmaril which his wife Elwing's grandparents, Beren and Lúthien, had taken from Morgoth. But Fëanor's sons still maintained that all the Silmarils belonged to them, and so there were two more Kinslayings. Eärendil and Elwing crossed the Great Sea to beg the Valar for aid against Morgoth. They responded, sending forth a great host. In the War of Wrath, Melkor was utterly defeated. He was expelled into the Void and most of his works were destroyed, bringing the First Age to an end. This came at a terrible cost, however, as most of Beleriand itself was sunk.