Hi Craig,
Enter the 'help' command to see a general description of the command line in PixInsight and a list of the commands currently available. To get extended help on a particular command, enter 'help <command>'. Unfortunately, we still have no official documentation for the CLI. Please feel free to ask anything related here.
The current command line interface is just a hint of what it is intended to be. It will be considerably extended in future versions of the PixInsight core application.