Guilt is a powerful theme in The Kite Runner. The central character, Amir, struggles a great deal with guilt, and he finally overcomes it at the end. An essay on guilt could discuss his guilt and his struggles with it, until he redeems himself. Let's look at what Amir has to be guilty about and how he does redeem himself.
Amir treats Hassan very poorly, doesn't he? We see him constantly looking down on Amir and treating him more like a servant than a friend. He betrays Hassan by not rescuing him when Hassan is raped by Assef and Assef's friends. Then he betrays him again by letting Baba think that Hassan is a thief. And Baba and he run away from Afghanistan, leaving Hassan and Hassan's ostensible father to die there. So you see, there is a great deal to write about when it comes to Amir's feelings of guilt.
When Amir finally returns to Afghanistan as an adult, he is able to face down Assef and rescue the son Hassan left behind, Sohrab. He is finally making up for all the wrongs he did to Hassan, and this redemption allows him to live a better life.
To write an essay about all of this, you will need to write an introduction, to introduce your reader to the book a little, the name of the book and the author, as well as a sentence or two explaining what the book is about, where it takes place, for example, and who the main characters are. You can end your introduction with a thesis statement, which should state what your main idea is about guilt in this book and list the points you are going to discuss about guilt.
Then you can write a body paragraph about each point, perhaps one about each reason Amir feels guilty and then one about how he redeems himself. Each paragraph needs to stick to just one point, and you can use evidence from the story about that point.
Finally, you will need one more paragraph, a conclusion, to remind the reader what your main idea is and the points that you made in your body paragraphs.
If you think about this, you will probably be able to find many examples of why Amir feels guilty about how he treats Hassan in this story. I have listed a few, but really, there are many more. The important thing is to state your opinion about guilt and then support it with evidence from the book.