This article is suitable for this script only: Classifieds Multipurpose Portal – Infinity Market

1. Add new category in Admin->Listings->Categories->Add New
   Screen: http://geniuscript.com/classified/documentation_infinitymarket/#!/add_listing_category
2. Add new related fields in Admin->Listings->Fields->Add field
   Screen: http://geniuscript.com/classified/documentation_infinitymarket/#!/listings_fields
3. Hide fields not related to your new category in Admin->Listings->Dependent fields->Add dependent field->check fields that you wish to hidden
   Screen: http://geniuscript.com/classified/documentation_infinitymarket/#!/dependent_fields

And this is everything… you should not unlock or remove any field at all because this will break other categories to work properly.