When you select an output folder, a master folder is created. Is there no master folder? The master files are in there.
DSLR, I presume? RAW files.
Were your master files calibrated/processed in any way in nebulosity, prior to importing them to the batch processing script?
Do you have a set of untouched raw files to use with the batch preprocessing script? That is straight out of the camera? Try those first.
With a little guidance, I'm sure that you don't need to purchase how to videos to evaluate PI.
Using untouched raw frames and using the batch preprocessing defaults for now,
Load your frames by tab - Bias, Dark, Flat, Light
Select a reference image from your light raw frames
Select an output directory
"Run" - diagnostics will alert you about any fundamental errors to this point.
Coffee, tea...
When all done your linear integrated image is found in the master folder of the output directory.
Hope this answers some of your questions