In the book it says that buck has to steal the food in order to stay alive. Where they lived if you waited to eat your food other dogs would eat it. Buck was confused why they dog stole his food but later on her knew why.
Helping each other
Buck learned that no dog can beat a man with the club. The man in the read sweater would go to the dogs again, and again, until he made then understand who was boss. They would sometime get beat till blood came out because they had to be taught to obey.
Spitz is the leader of the dogsled team. Buck is the only dog to seriously rival Spitz as leader. Many of the of dog thought that spitz was strong so they did not want to rival spitz.
Staying in good health
John Thornton turns out to have had frozen his feet during the previous winter. Also his dogs are now waiting for the river to melt and for a raft to take them down to Dawson. So buck stayed with him the whole time.
All of the dog were in holes they dug in the snow. A spot that keep them warm. At some point if they did not know what to do they would get frost bite.
Dolly was a dog in the group that gets sick from a bite from one of the starving huskies. he goes mad and attacks Buck. So they could not let it spread so Francois has to kill her so she would not pass it down to other dogs.