Add a "post form data to forum" feature to a mod?
 

I am new to this but have been researching a way to modify a store front mod. I want to replace the payment button function with one that would post the sale info to a specific forum.

I know this is pretty vague, but does anyone know where I should start looking to build the posting part? Code example would be great too.

You could add a hook to the newthread_start, I think.
I am also new to all this so someone else may give better detailed instructions.
There is a Form Hack that posts a form to forum or thread, with PM and emal options.
You may look into how the plugin is coded.
https://vborg.vbsupport.ru/showthread.php?t=126676