Very little theory is necessary to begin to understand music through piano playing because theory is expressed in good music, gradually with each level.
We can become aware of this as we play. There are some basic tools: scales, arpeggios and chords teach us how to spell and group notes.
These are available in the technical library. Form and chord progressions become familiar with repeated listening. Bass motion by repeated intervals is something we can typically notice.
usschoolofmusic.com/lucky/TPG/MUSICTHEORYMUSIC THEORY usschoolofmusic.com/lucky/TPG/MUSICTHEORY