If you mess with a keyboard for long enough, you'll probably find yourself making up some of your own music, and also sometimes just randomly noticing a sequence of notes that sounds familiar and tweaking it until you figure out how to play something you've heard

Some people get skilled enough to just watch what other people play in person or in videos and then kinda copy what they see

The Suzuki method teaches music without reading. The theory is the same as how a child learns a language, through listening first before reading