We have some great resources that explain how to edit an existing form as well as a Getting Started Guide that goes over how to make use of the new features of this tool.
The validations are applied with our client or server side validations wizard, you can apply this from within the Form Builder interface or from the Insert > WebAssist > CSS Form Builder menu.
Here is a link to the support page, the editing forms how to is in the How To section, the getting started also has some great info.
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