I'll answer the second question first, because it has the easier answer. I have no clue. Stuff comes to me and I put it down on paper or into my computer after I let it percolate in the back of my mind for some non-specific amount of time. For some stories, it's a few days. For others, it months or years. This part of the process is a mystery to me, as I think it is for most writers.
Now to the second question, which has a much more concrete answer. First off, let me say I hate this question. The question is so loaded with expectations, especially during my time at San Francisco State University where everything was so focused on Literary Fiction and creating works of art that when asked this question, which we were frequently, the pressure was on to come up with some noble reason or purpose we were dedicating ourselves to with our fiction.
The truth is, I just want to entertain people. Yeah, I could go on about holding a mirror up to the human condition and exploring unanswerable questions and offering up examples of moral gray areas, etc, which I do a lot in my fiction, sometimes consciously, as with the Tears of Rage books, and sometimes unconsciously, as I discovered when I went back through Halloween Jack and the Devil's Gate. I find those things interesting, but they are not my motivation for penning fiction. It comes down to wanting to entertain people. I write stories that I wish other people had written so I can read them. I like cool stories, and that's what I try and do with the stuff I write, make them so cool that I get a thrill every time I go back and read them. I know some writers don't ever go back over their own works once the work is published. I can't imagine doing that. I just reread some of Halloween Jack and had a blast with it.
So there you have it, the reason I write: I want to write cool stories. If my work resonates on a deeper level, that's cool too, but has nothing to do with what got me started on this road. If the work doesn't go deeper than being cool, I'm okay with that, as long as someone is entertained. If I hit that mark, I'm all good.