how do you do it? I don't know any other ways.

Not BSO, when I was a kid, i was busy and my parents were very busy too. We didn't have a piano in our house(don't know why) until one day my parents saw me sang a piece of music i never heard before from a music sheet.  Up until then, all the music lessons i had were just regular music classes in elementary school.  Basically, i just had figured it out by myself with the sound of music in my head.