There and Back Again is the title of
Bilbo Baggins'
memoirs, in which he records the events of the story that we know as
The Hobbit.
Tolkien wrote all his
middle-earth stories with the
conceit that he had found books from an ancient culture written in an ancient language, and translated them into our world's langauges -- the common language became
English, and the other languages became invented languages which preserved the feel of the original from the perspective of someone who spoke the common language. For example, the language of the
Elves sounded foreign, musical, and complex to the ears of the
Hobbits, so Tolkien invented a language based on
Finnish, which sounds that way to English-speakers.
The Hobbit is thus the contents of
There and Back Again, with some explanation and
framing story added by the "translator."