If you're familiar with c or basic, then you aready know the basics of for/next and if/then scripting. .FPI was written for the FPSC engine and will probably never be used beyond that. I think there are some tutorials floating around by different members, but nothing by the authors that I know of. After all, it was meant to be drag and drop/WYSIWYG.
That being said, FPSC is still in it's infancy and there are many good people working to improve it, including of course TGC.
Looking at the scripts and figuring out how they work has helped me a lot. Once you see what the script is doing, it's easy to alter or re-write completely. Experiment.... have fun with it. Just make sure to save the originals.
Happy scripting.
Crazy Grandpa