There are three approaches that can be employed when designing web forms:
Form-First: You can follow a "Form-First" approach where you create the form first before any data elements are defined and you let PCS by just drag and dropping components from the component palette to the page.
Data-First: A data-first approach implies a bottom-up approach where you create a web form based on data sources or business objects by just drag and dropping the objects on the form to create controls.
In the "Business Types" section you can import your XML schema definition files (XSDs) which you can then use in your web form.
Hybrid (Data-First and Form-First): The third and last approach that you can follow uses a combination of the above two approaches, that is a hybrid data-first and form-first approach.
You can create soma parts of a web form from scratch while other sections can be based on existing data sources and data objects.