This is a character piece from the Brazilian piano repertoire. It features a simple melodic structure typical of late 19th and early 20th-century salon music.
The primary challenge is shaping the melodic line with a singing tone while maintaining a steady rhythmic pulse.
Comparable difficulty and character — good candidates for what to learn next.
21 de abril is rated Henle level 3 of 9 — late beginner repertoire, roughly ABRSM grades 4–5. In the RCM system it corresponds to about level 4.
You should be comfortable at Henle level 3 — meaning you can already play level 2–3 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 21 de abril lasts about 2 minutes.
21 de abril is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.
Pieces at a comparable difficulty and character include Bonita como eu só... by Carlos T. de Carvalho, Amar... só a ti by Carlos T. de Carvalho, 1914 by Carlos T. de Carvalho — see the full similar-pieces list on this page.