Click Script INCLUDE on the SYSTEM ribbon panel to display the Insert Script INCLUDE window.
Read more: Command Syntax
You must press Insert (or Update if editing an existing command) for your changes to be applied to the current script in the editor.
Do you find that some of your custom report scripts are always the same? Perhaps you are using a header with the Kingdom Hall address etc. and you put this at the top of several reports.
If this is the case, then consider putting the script that gets repeated everywhere into its own custom report. Then, you can use the Insert Script INCLUDE facility to insert the script at the cursor location.
You are presented with a list of your existing scripts. Simply select the one that you want to include and press the Insert (or Update) button. As you select a script you will see it's contents displayed below.