PloneFormGen represents a form as a folder and fields as items within it, which lets it inherit a lot of its user interface "for free" from Plone. To start a new form, pull down the Add new menu anywhere in a Plone site, and choose Form Folder.
Note
Easing the mental mapping for users
Though it simplifies the codebase, the way forms behave like folders is not always intuitive for less technical users; some will need a bit of training and acclimation. For larger organizations, it can help to have a Form Czar or two: community-minded power users with people skills who can render informal first-tier support and training.
After you add a form folder, a page of options will appear. For now, just set the Title to Contact Us, and click Save at the bottom of the page. To give you a jumping-off point, PloneFormGen adds not just an empty form folder but enough within it to provide a simple contact form: email address, subject, and a field for comments. If this is what you want...