Well, I've been involved in eight plays over the course of the last four years up there, so I suppose I'm sort of qualified to tell you a little bit about the process. Basically, there is no definitive way; if you have a show you want to put on, apply to various venues around January-March time, who will then either offer you a slot and let you know costs, etc, or turn you down (which doesn't happen that often in my experience). It's then a matter of raising money, which can be done by getting sponsorship from companies, using your own money which you can then reclaim when the ticket sales money comes through, or getting paid for pre-Edinburgh performances at local venues. It can be a bit daunting first time round, but is worth it in the end, the Fringe is one of the most amazing experiences in the world, I want to go back every year for as long as physically possible. Good luck!