I think it will show in the navigation if the application is enabled and you tick Show in Nav on the Applications page.

However, my favourite way to add a custom form to a page is to actually use the Survey tool to create the form, but then instead of showing the survey tool in the nav you can embed the form using the Survey includelet onto a page of your choice, anywhere on the site. This is something you can't do with the form builder (unfortunately!)

More info about the Survey tool here. Or ask Voicebot! :-)

Thanks

Joe