A lot happens to Buck after he leaves Judge Miller's house. I want to make it clear though that Buck did not leave the Miller house by his own choice. Buck loved the Miller family and they loved him. Unfortunately the gardener, Manuel, does not love Buck that much and has a gambling debt. Manual "dognaps" Buck and sells him. From there Buck is transported in a cage to an unknown destination via train.
Eventually Buck is let out of his prison by a man in a red sweater . . . and a club.
A stout man, with a red sweater that sagged generously at the neck, came out and signed the book for the driver. That was the man, Buck divined, the next tormentor, and he hurled himself savagely against the bars. The man smiled grimly, and brought a hatchet and a club.
The man in the red sweater calmly used the hatchet to free Buck from his cage, and he then picked up the club. Enraged at having been mistreated for days, Buck attacked the man in the red sweater. Each time that Buck attacked, the man defended himself and hit Buck with the club.
A dozen times he charged, and as often the club broke the charge and smashed him down.
Buck continued to charge and attack until he was beaten senseless. The encounter with the man in the red sweater was Buck's introduction to the "primitive law" that will become important through the rest of the novel. The law is "might makes right." As long as that man held the club, he held the power.
He was beaten (he knew that); but he was not broken. He saw, once for all, that he stood no chance against a man with a club. He had learned the lesson, and in all his after life he never forgot it. That club was a revelation. It was his introduction to the reign of primitive law, and he met the introduction halfway.
The next thing that happened to Buck was waiting. Buck saw other dogs come and go as they were bought and sold by the man in the red sweater. Eventually a man named Perrault buys Buck, places him on a ship, and takes Buck north where he encounters snow for the first time. That will end chapter one.
At the first step upon the cold surface, Buck’s feet sank into a white mushy something very like mud. He sprang back with a snort. More of this white stuff was falling through the air. He shook himself, but more of it fell upon him. He sniffed it curiously, then licked some up on his tongue. It bit like fire, and the next instant was gone. This puzzled him. He tried it again, with the same result. The onlookers laughed uproariously, and he felt ashamed, he knew not why, for it was his first snow.