At the end of the second section, the firemen get a call to go to a house reported to hve books. The house is Montag's and he is required to burn it down.
Beatty required him to burn down his house by pumping the kerosene and using the flamethrower himself. Beatty took the "green bullet" from Montag and started to antagonize him. In the scene, you can see that Montag had enough and torched Beatty. This was the turning pointin the story.
Once Montag was out of the heat and on the run, he went to Faber's house to say thanks, with the Mechanical Hound following. Faber gave Montag new clothes, and Montag gave him some money in return.