I realize I may have left out something key to understanding dBFS for the unfamiliar. Unlike with dB SPL, which is what you are referring to with “at audible 0dB,” zero dB refers to the loudest possible sound in dBFS. The unit stands for decibel relative to full scale, where full scale (loudest possible sound) is 0 dB. So in dBFS, unlike with dB SPL (sound pressure level), all audible sound is stored as a negative dB value. When you listen to the audio file, this is first converted to a voltage, and then to sound pressure, which is finally measured in positive dB SPL.

If that doesn’t explain it for you, I don’t know what you don’t understand, and I can’t help. I would recommend finding some YouTube videos on the subject, in case you’re a visual learner.