The main conflict in the book Holes was that Stanley was sent to prison for something he did not do, and it was resolved when he helped shut down Camp Green Lake (and found out Zero took the shoes).
A conflict is a struggle between opposing forces. In this case, Stanley faces a character vs. society conflict over being sent to prison for something he does not do (and being cursed).
There are different conflicts in the book in different time periods, but all are interconnected. You could say that the overall main conflict is that Stanley’s family is cursed, and he broke the curse when he carried Zero up the mountain. More practically, the main conflict is that Stanley is accused of stealing a famous ball player’s sneakers and sent to Camp Green Lake.
Camp Green Lake is an abusive place. The warden is a sociopath, and her employees are either clueless or sadistic. Stanley can do nothing but try to make the most of his time there. It is not until he befriends Zero and then runs away with him that he realizes Zero is actually the one who took the shoes, because he was homeless and just needed good shoes. He did not keep the shoes because they smelled bad.
“I should have just kept them,” said Zero. “I’d already made it out of the shelter and everything. I ended up getting arrested the next day when I tried to walk out of a shoe store with a new pair of sneakers….” (ch 41)
Zero just thought he was taking an old pair of shoes. He did not know they belonged to a famous person. Zero never intended to be bad. He just took what he needed, because that is what you have to do to survive when you live on the street.
Stanley found out the long-standing connection between his family and Zero’s, and broke the curse. He also freed Zero from the never-ending prison of Camp Green Lake, and shut the camp down and the warden as well.
With this conflict and the others, Sachar is demonstrating one of the major themes of the book--that everything is inter-related. One thing can have long-standing consequences that you don't expect, and the past always affects the present.
The main conflict in the book Holes was being cursed. He was cursed by a long relative in his family because he lied to a fortune teller/witch. Stanley was sent to a camp because he was blamed for the stolen shoes. He soon resolved the curse by turning the camp around and finding Stanley's mom.