Last question, what is the climax of the story? And how do you know that this is the climax?

The climax comes at the end of the story when Rainsford confronts Zaroff in his room. Zaroff, caught, tells Rainsford he's won the game and is free to go; Rainsford on the other hand, decides the game isn't really over and kills Zaroff. We know this is the climax because it is the most exciting, intense part of the story.