Just write. Don't worry about any of the other crap for now, that will come later. Just write, for yourself. Don't worry about what might happen when you're done, or if other people will like it. Right now, all that matters is that you're spilling your brain onto the page.
This first thing you write, it may never see the light of day. But until you have written at least one piece, you'll never know where you are and how far you need to go.