What you need for this book
Unlike many other technical books, this one focuses on a wide variety of supporting technologies in its examples. I don't expect that you'll have experience or the tools to try every example in this book, especially right away. However, it's helpful to have a few things set out.
You should have some programming experience, preferably in JavaScript. Unless a recipe is targeted at a specific programming language such as C#, the recipes in this book are written in JavaScript. I do this for two reasons. Firstly because the "J" in JSON stands for JavaScript (even though it's widely applicable to other languages), and, in this day and age, every programmer should have at least a nodding familiarity of JavaScript.
As far as software environments go, to begin with, you should have access to a good web browser such as Chrome or a recent version of Safari, Firefox, or Internet Explorer. You can use the JavaScript runtime in any of these browsers to experiment with JSON and get started.
Secondly, a lot of the client-server examples feature Node.js. I picked Node.js for server-side example programming because it's also JavaScript, meaning that you don't have to jump through different language syntaxes as you move between the client and server. Node.js runs well on Windows, Mac OS X, and Linux, too, so you shouldn't have a problem setting it up.
If you're interested in using JSON with databases, CouchDB or MongoDB are your best choices and I discuss both of them in this book. Which one you choose is really a matter of your domain and personal preference. I've been using MongoDB for 5 years on various projects but have recently taken a liking to some of CouchDB's features and its integrated support for RESTful services.
Finally, if you're a Microsoft developer, you may want to take special note of the C# examples that use Newtonsoft's Json.NET throughout this book. Json.NET is what JSON in C# ought to be, and it's definitely worth your attention.