One-shots, chords and loops
Piano samples come in three shapes. Single notes are the building blocks of a sampled instrument and are usually named by pitch, such as C4. Chords and stabs are ready to drop into a beat. Loops and phrases are complete musical ideas, often with a tempo and key.
University and orchestra libraries recorded every note of a concert grand at several dynamics and released them for free use. Those are ideal if you want to build your own instrument. For beats, a chord stab or a short loop gets you started faster.
Before you release
Note-by-note recordings from public institutions are often public domain or CC BY. Loops on community sites vary widely. The badge on each card tells you if it is cleared for a release and if you need to credit the recordist.