Thereupon Hanuman said, ‘O represser of foes, even to the extent of thy curiosity to know me, shall I relate all at length. Listen, O son of Pandu! O lotus-eyed one, I was begotten by the wind-god that life of the world—upon the wife of Kesari. I am a monkey, by name Hanuman. All the mighty monkey-kings, and monkey-chiefs used to wait upon that son of the sun, Sugriva, and that son of Sakra, Vali. And, O represser of foes, a friendship subsisted between me and Sugriva, even as between the wind and fire.

In plain words: Hanuman agrees to tell his story. He says he is Hanuman, son of the wind-god and the wife of Kesari. He was a close friend of Sugriva, a monkey prince, in the time of the monkey kings Sugriva and Vali.