Short answers, pulled from the story.
Aristotle's Metaphysics is a collection of fourteen books developing what Aristotle called First Philosophy, the study of being as such and the ultimate causes of all reality. It covers substance theory, the principles of contradiction and excluded middle, the unmoved mover, and the philosophy of mathematics.
The title was not chosen by Aristotle. It derives from the arrangement of his works by Andronicus of Rhodes in the first century BC, in which these treatises were placed after the Physics. The Greek word for "after" is "meta," giving the collection its name. Aristotle himself called the subject First Philosophy.
The Metaphysics consists of fourteen books, referred to in manuscripts by Greek letters from Alpha to Nu. W. D. Ross, in his 1924 edition, concluded that ten of the fourteen form a more or less continuous work, while the remaining four were inserted by later editors.
Avicenna wrote that he read the Metaphysics forty times and memorized it before he could understand it. He said he had despaired of ever comprehending it until he read al-Farabi's book on the objects of the Metaphysics, which he found by chance at a bookseller's quarter one afternoon.
The unmoved mover is Aristotle's concept of a first cause that is itself uncaused and eternal, described in Book Lambda. Aristotle calls it "the most divine of things observed by us" and characterizes its activity as "the thinking of thinking." It is eternal because only created or destroyed things require a cause.
Alexander of Aphrodisias wrote a commentary on the first five books in the 3rd century. Themistius wrote an epitome, of which only Book 12 survives in a Hebrew translation. The Neoplatonists Syrianus and Asclepius of Tralles also wrote commentaries, attempting to reconcile Aristotle's doctrines with Neoplatonic cosmology.