Guidence help for Pro Form

I need guidance to do the following:
I managed to get a list of categories using Select - Option. How can I create a condition so that by choosing one of the categories, I get fields for Post Submission in that particular category? Do I create a separate Pro Form for each entry or is everything done in one Pro Form? And how can I get the condition to get the requested fields only for the selected category? I use JetEngine, everything works great except for the attempt to have the site owner do the entry of posts on his own. Thanks for your answers (if any)…