[cranjice]

Knowing which keys to press translates loosely into an understanding of theory (even at a very simple level)

Think of the piano keys (chromatic scale) as the alphabet, and theory as the language that makes words from it.

Tbh a little theory goes a long way. It’s all related and your understanding will build over time. You’ll start to see patterns.

Just start off learning how to play a simple song. Then, try to think about what key is this song in? What chords make up that key? What intervals am I playing? How would I transpose this song into a different key? Etc.

You can teach yourself, but a teacher or good course will accelerate the process.