There is simply an infinite amount of levels to it. You might start off by just being able to recognize the difference between a minor and a major third. Then y

There is simply an infinite amount of levels to it. You might start off by just being able to recognize the difference between a minor and a major third. Then you expand that further. And to recognize what note it is relative to the scale. At some point children's tunes become easy. At another you recognize the specific chords in children's tunes. Then you expand that to be able to identify the notes in more complicated tunes. At one point you might pick up jazz... The point being that at any point in time during your development you will feel mastery of some level of melodies/chords/harmonies but feel utterly confused (tone deaf) by more complex ones. It's an infinite journey and the key is enjoying it, there is no final destination.