Why do people write and how? Well, first you get inspired by one idea. If you got plenty of imagination, it's easy to build up the idea in your head. I suggest you start to write some of this huge imaginary plot, you carry, down on paper or on the computer.
When you have chewed on the idea, try to talk about it to a friend, there is great additional inspiration and later you have to decide: Am I going to follow this through? Am I going to tell this story?
Your ideas might not come in a sequence, so you have to administer what fits into what and in what time. Look at it like running around with a digital camera all over town and taking pictures of things you like. When at home you look at them in different ways and if your good at making order, you categorize your photos.
Same with all ideas you get for one story. In simple explanation, you can have a folder in your livingroom and separate pieces of paper for each idea. You can have several folders as well, one folder for each story.
You get new ideas and write it down, print it, maybe, and you categorize these into your folders. The best is of course to have a digital copy, so you don't have to rewrite everything.
The driving force or life force of a story is that your overall idea about the whole story is more or less finished.
When you carry this big story and fiery plot in your head (and hopefully, already wrote something down), you are ready for the big job: Writing and rewriting. You put it all together. New ideas comes to you, so better make it as good as possible from start. The easy start of a story is all about, that you know the ending, the plot, the secrets.
