I believe you are refering to the preface and letters that come before Victor's narrative begins. The preface was the author's telling the reader that the story was conceived during a vacation, where literary figures met and had a competition on who had the best horror story.

The letters, which are four in total, are written by a rich English explorer, Robert Walton, to his sister Margaret. In these letters he tells his mini-story on how he is stranded somewhere searching for Earth's magnetism.  It is in these letters that he tells her about him meeting Victor, about seeing this "creature" near Victor, and it is when the actual story begins.