You can write FabEngine Scripts in any text editor. To do something useful with them, you will need a FabEngine account. If you haven't done it yet, you should sign up for FabEngine here. It's free.
We've put together three simple example FabEngine Scripts with lots of inline comments. When you sign up for an account, these scripts will be pre-loaded into your dashboard, to get you started. Have a look at them! It should give you a pretty solid idea of how FabEngine works.