The main exposition in the novel Frankensteincomes in the form of the letters that Walton sends back home to his sister. These letters tell of his adventures trying to explore the Arctic regions, seeking to find a water passage. This is where the character of Victor Frankenstein is first introduced to us. The actual story is then told in frame narration as Walton tells the story that was told to him by Victor.
Walton's letters also introduce the themes of human desire, man pushing the boundaries of nature, human conquest, etc. These topics continue and are used throughout the novel as we hear Victor's story. Victor warns Walton not to make the same mistakes.