The Create New Script dialog is accessed using the New command from the script management dialog.
The list on the right lets you select the various script events that you want to implement in your new script. Opus will create boilerplate code for all selected events. You can add additional events later if you need to.
At the bottom of the event list are the entries NewScriptCommand and NewScriptColumn. These are placeholders for commands and columns that you want to implement in your script. If you turn one of them on, Opus will prompt you to enter a name for the new command or column. It will then be added to the event list in its own right, and the NewScriptCommand / NewScriptColumn entries will be available again to add more commands or columns. The boilerplate code for any commands/columns you specify here will be created automatically.
Once the new script has been created the script editor will open automatically.