"There and Back Again" is the name that the fictional character Bilbo Baggins would give to the book about his adventures. Tolkien would name the work "The Hobbit".
Although Bilbo was not especially aware of the fact, Hobbits are remarkable creatures. Also called "Halflings" they stand about half the height of a man, are very sedentary 'til roused, have a thick, bushy crop of hair on the top of their head and on the top of their leathery feet. (Conveniently, they are never in need of a new pair of shoes.)
"The Hobbit" is a children's book. Originally, it was written for Tolkien's four children, who loved every aspect of the story. It is a book even adults like to read...again and again. Tolkien, himself, was a University of Oxford Professor. He was a philologist, a lover of language, who at a very young age began to develop his own languages. "The Hobbit and his other works largely grew out of this love.
Bilbo Baggins is aroused from his comfortable Hobbit hole (not a messy, wormy hole, but a cozy place with windows, rooms, cupboards, and fireplaces). He is visited by Gandalf the Wizard and 13 Dwarves on an adventure. They are looking for someone to act as a thief or perhaps a scout, for they are going to attempt to retrieve the treasure amassed by Smaug the Dragon.
As choices go, Bilbo is a curious one for Gandalf to have made for a thief. Bilbo is an honest, decent fellow. Yet he has certain latent qualities that suit him to the job, not the least are his courage, intelligence, wit and natural Hobbit stealthiness. Bilbo is determined not to participate in this "harebrained" scheme. Nevertheless, he is somehow roped into it and begins his adventure, without his handkerchief, an item he sorely misses.
The handkerchief represents all the comforts of home. "The Shire", where Bilbo resides, represents England, and Bilbo Baggins himself represents the doughty race that resides in that country.
The adventure, "There and Back Again", takes Bilbo, Gandalf, and the Dwarves through various locales as they meet up with sundry persons and peoples. The Hobbit is, indeed, a children's story. Yet it is so packed with plot, dialogue and history that adults cannot help but to be drawn into it. Many aspects of the adventure are based on Scandanavian mythology. Mirkwood forest is borrowed from Icelandic mythology. (Mirk means "border") The names of the Dwarves are borrowed from Norse place-names. Even the form of the story has the quality of the saga about it.
In the end, it is the story of the average person, a person who loves his creature comforts, and yet is stirred to do great things by the forces of destiny and his own indomitable will.
While "The Hobbit" is a complete and light-hearted story in itself, it sets the scene for Tolkien's adult work about Middle-Earth The Lord of the Rings.