23-2: un corneta: the nouns corneta, trompeta, etc., used in the feminine, denote the instrument, and in the masculine, the player.
24-1: sabré música: ordinarily the definite article is used before a noun employed in a general sense. Here a partitive sense is hinted: I shall know (some) music.
25-1: mi vida se reducía a soplar: I passed all my time in playing (soplar, to blow).
25-2: notabilidades: noted men; celebrities.
25-3: al ave: el replaces la before feminine nouns beginning with accented a or ha. Un is occasionally used for una in the same cases (not academic).