who introduces Antonia to the reader?

The first-person introduction is written in the voice of a childhood friend of Jim Burden, who is the narrator for the remainder of the novel. So I guess you could say the narrator is anonymous. The introduction of My Ántonia is called a frame, or framing device. It is a preface for the novel, and it is written in a voice other than the one that narrates the body of the text. It is called a frame because it provides a very specific context for the novel itself, and it forces the reader to see the novel from a certain perspective. Because it is written in the voice of an anonymous, relatively insignificant character, it creates a distance between the reader and what he is about to read. In creating the folder labeled "My Ántonia," Jim was writing primarily to himself, not to a larger audience