If you install the script file and Photoshop actions as instructed above, it should work out of the box.
It is meant to be run by using one of the ready-made actions that comes with the script file, or by a droplet made from one of those actions. I’ve provided a starter set of actions, grouped by aspect ratio, as well as a folder of exploration actions, meant to show a few additional script options.
If you want to, you can stop reading now and start playing with the actions, or you can read on and learn how to create your own actions, batching folders of images and troubleshooting.