Short answers, pulled from the story.
The Nannerl Notenbuch is a notebook that Leopold Mozart filled with keyboard pieces for his daughter Maria Anna Mozart, known as Nannerl, from 1759 to about 1764. Wolfgang Mozart also used the book, and his earliest compositions were recorded inside it.
Leopold Mozart presented the notebook to Nannerl on the 26th of July 1759, marking her eighth name day. Some accounts suggest the true occasion may have been her eighth birthday instead, on the 30th or the 31st of July.
The notebook originally held forty-eight bound pages of music paper, but only thirty-six remain today. Twelve pages were removed over the years, and eight of those have been identified in other collections by Alan Tyson.
Leopold Mozart wrote more than half of the notebook's contents himself, alongside two or three anonymous Salzburg copyists later identified by Wolfgang Plath as Anonymous I, Anonymous II, and Anonymous III. Wolfgang Mozart also inscribed some pieces in his own hand, including his first self-written entry, the Klavierstück in C, K. 5a.
Wolfgang Mozart's first composition was the Andante in C, K. 1a, a piece just ten measures long written for the harpsichord. It appears in the notebook alongside later pieces such as the Allegro in F, K. 1c, composed on the 11th of December 1761 in Salzburg.
The notebook contains a table of intervals and modulating figured basses, showing that Leopold Mozart taught music theory and composition from his children's earliest lessons. Piece number 48 also shows him teaching by example: it arranges his own Serenade in D, whose trio reappears as Menuet II in Wolfgang's Sonata, K. 6.