By opening the project overview page https://flyingforms.io/Space and clicking on your project.
After clicking on Create, the form designer will be open directly. And you will see an empty form configuration.
The form is working with sections that can be added by clicking on the + icon. Each sections can contain fields like single line, checkbox and so on.
After setup field you need a submit action as a minimum setup. The minimal setup is to send a notification. Follow this guide on /Developer/SendNotificationOnSubmission.