If you really didn't know anything about music, you wouldn't want to learn how to play. If you've been listening to music all your life, then you probably know a lot about music. If you didn't know these things, you wouldn't bother to listen to music.
You can find the tonic (the 'one-note' or 'bass note') of the song.
You can tell whether a note is higher or lower than another.
You can find the basic pulse of a song.
You can identify the accented beats in a measure.
You can tell when one chord changes to another.
You can find and anticipate the downbeat of a measure.
You can tell the difference between major and minor.