How can I add an extra value to a contact once the form is completed?

On the back end of a form, you have the option to save an extra value when the form is being processed. For instance a language. You will find this option in the form properties. Here you can choose from all database fields in your account. Do you want to save multiple values when a form is being processed? If you can the Module Campaigns, automatic campaigns allow you to save multiple values at once.