Designer Desk is different from a lot of tools in that it doesn’t want you to build the application. Instead, it helps you describe the application in the best way possible.
Your form, workflow, etc. become a prototype, a living example of what you want the application to look like and how it should behave.
Try it out yourself. If something’s not quite right – change it. Add notes to it like “the end time must be at least one minute after the start time, and by default, it starts tomorrow at nine a.m.” Try it again. Change it again. Until you don’t need to change it anymore.
You can have application builders look at your prototype. You can even click one button and produce thorough documentation that tells them what they must do to build what you designed. They’ll turn your diagrams and notes into rules, formulas, script, and sometimes even actual code – but that’s their job. Yours is done.