What's the difference? When I use "to" or "for"?

Bookreview I was writing a bookreview for my English class and i need your help... I Am Not A Serial Killer by Dan Wells tells the story about John Wayne Cleaver, he’s 15 years old and whom lives and works with his mother at a mortuary. He has been diagnosed with antisocial behavior, this means that … John will be a serial killer in the future; he tries to be normal but he isn’t, because he hasn't feelings and he want to hurt toward others, including his family, so for this reason he has a rules for control his actions, because John knows that he’s destined to become a serial killer. But the things changes to John when in Clayton appears a Serial Killer, so… John throws his rules to the trash, because he wanna knows who is the serial killer, this obsession change his mind and start the game for him. The Clayton’s murderer has a different patrons than others killers, and John doesn't know for why reason, so…this is a play game for him and he’s like a FBI agent, but he has a reason, he wants to kill the serial killer, but he doesn’t know who is the murderer. The killer is more near than he imagined, but when he recognizes the killer serial intentions is too late. John lost so many things for his fails in the investigation, but now he knows who and what is the killer; The murderer is a demon and John tries to kill the killer. But the things didn't end to John…