Since you are writing a short essay, you probably should focus on one theme in the short story and show how it is developed, using examples from the story for support. The theme in this story is developed from the main conflict, the man pitting himself against nature. He loses, of course, and he freezes to death, but his dog survives. The conclusion of the story suggests that the dog survives because of its natural instincts, while the man's human judgment is no match for the forces of nature.
You could write your essay to show how this theme is developed in the story. Look for examples of the dog's instincts at work and how they keep the dog alive. Then look for examples of the man's poor judgment and how his failures in judgment lead to his death, how he is overpowered by nature. Through a careful reading of the story, beginning at the very beginning, you will find many examples to include in your essay. Also, you will find below several links to enotes resources that should help you a lot. Good luck!