Creativity is an elusive concept; explaining how it works is intensely personal. I'm always fascinated by individuals' understanding of the process.
If you're in Australia, I recommend you watch Matilda and Me on iview (it's available there until 18 April). It's the story of Tim Minchin and how he came to write the music for Matilda: the Musical, a most wonderfully joyful musical, which I thoroughly loved.
I was taken by his description of his process and how all his creativity comes out of his head through his fingers and into the piano keys. Wonderful viewing.