First things first: The Adventures of Tom Sawyer is going to focus primarily on Tom Sawyer. The young (we're talking elementary school age) native of St. Petersburg, Missouri has a liking for escapades, exploits, deeds of derring-do, or what you might call adventures. Note that the book is called The Adventures (with emphasis on the plural) rather than The Adventure of Tom Sawyer. Little Tom gets up to a lot of trouble by book's end, and his various feats are not all related.
The book's what you might call episodic, telling a bunch of little stories instead of sticking to one main adventure. Some of Tom's adventures are long, taking chapters to play out; others are begun and finished in the span of a few pages. As such, you might already be familiar with some parts of the story – the famous whitewashing scene, for example – without knowing anything else about he book. The scenery changes, as does the cast of characters, but Tom's always there, for better or for worse, front and center.