To get started, all you need is a text editor.
If you use a Mac, you can use TextEdit (under "Format" menu, select "Make Plain Text"), and if you use MS Windows, you can use Notepad. I'm using Atom Editor, and there are plenty of other cross-platform, open source options out there.
Knowledge of JSON will be helpful, but you should able to follow along regardless. If you get stuck, take a look at the complete transcript in the appendix.
I've added technical asides for experienced developers, but they are not essential to the tutorial, so do not be concerned if they do not make sense to you.
(Hint: while JSON is very forgiving about spaces, the standard is unforgiving about the presence and absence of commas. Look at examples carefully, and check for missing or superfluous commas.)