how does it work you ask? say you wanna write a fast up beat tune, you sure wouldn't use Eb. cause Eb is more of a mellow sounding note, i would use either C or G. or you want to write something that graps people attention, write something in F# or C#. it's gives you a better understanding of the notes and what they mean. Each note has a different feeling to it. To understand play a chromatic scale, listen to each sound. as see if its mellow, sad, happy, dark, and listen to the kind of feeling you get from it. that gives you the feel of each note. to discriminate between notes develops as you learn their differences. you just have to listen man.

mozart himself began playing the piano by just striking a note over and over until he could hear the note in his head.