To see the commands you can use with Script Editor:

Choose Window > Library.

Double-click Script Editor.
Script Editor is a scriptable application. It responds to AppleScript commands that let you automate Script Editor. You can edit, compile, and save AppleScript documents. You can even write time-saving scripts to help you script. For example, you can call a script from the Script menu that adds elements to the AppleScript you are working on.
Choose Window > Library.
Double-click Script Editor.
The Script Editor dictionary opens, showing the commands and objects that are available to script in this application.