In J.R.R. Tolkien’s The Silmarillion, the first major era of Middle-earth is called the First Age. It is also known broadly as part of the Elder Days, but “The First Age” is the specific numbered answer.
The First Age contains the wars against Morgoth, the first Dark Lord and master of Sauron. Major events include the return of the Noldor to Middle-earth, the stories of Beren and Lúthien and Túrin Turambar, and the catastrophic War of Wrath.
Tolkien’s chronology can be confusing because different texts use overlapping names and divisions. The Years of the Trees and the Years of the Sun describe earlier periods in the history of Arda, while the First Age is a later historical designation. The Silmarillion, edited and published by Christopher Tolkien in 1977, gathers much of this mythology from Tolkien’s posthumous writings.