This book 'Special Educational Needs - Getting started with Statements' by Tania Tirraoro explains it all ...
Had I known of this book when I started out, I will no doubt have saved at least 6 months of the process. And it also would have avoided me falling 'victim' to an incredibly dishonest solicitor whom I thought had my child's best interest at heart.
Please, do me a huge favour and get a copy of this book to get you started.