Following are a few preliminary hints about Mozart's music:
Languages: Mozart's native language was German, but he also wrote some secular vocal works in Italian, which was the language widely considered in aristocratic circles of the day as the "better" language for sung musical works. Mozart also composed many sacred vocal works in Latin.
Principal Vocal forms used by Mozart:
Principal Instrumental forms used by Mozart:
And chamber music for a variety of instrumental combinations.
Few of the instrumental works were originally published in collections or with distinctive titles, so watch for form titles for most of the instrumental compositions.
Numberings: Each work by Mozart is identified by a "Koechel" (pronounced Ker'-shul) number, named for the man who compiled the first systematic chronological catalog of Mozart's works. Since few of the instrumental works have distinctive titles, these Koechel numbers (always predeced by a "KV" for "Koechel Vezeichnis or "K" for "Koechel") can be very important for identifying exactly the work you want. For example, the Symphony no. 41 in C major (popularly known as the "Jupiter" symphony) is more precisely identified as "KV 551".
If you do not know the Koechel umber for the work you want, or if you do not know the original language of a work with a distinctive title, you can find these in most lists of Mozart's works, such as the one in The New Grove Dictionary of Music and Musicians, or in the Koechel catalog itself (in German). These sources are found in the reference section of the library. A librarian can help you find these, and show you how to use them.