These are likely short, characterful pieces by Mozart, possibly from pedagogical collections or less frequently performed works. They would showcase his characteristic clarity and melodic charm.
Focus on clean articulation and graceful phrasing to capture Mozart's elegant style.
9 Stücke für Klavier is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6. In the RCM system it corresponds to about level 4.
You should be comfortable at Henle level 4 — meaning you can already play level 3–4 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of 9 Stücke für Klavier lasts about 10 minutes.
9 Stücke für Klavier is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.