When you use compact form fields, the field name or the label of the field will be displayed within the input box or text area. The text will disappear as soon as your form visitor starts writing in it. This feature can be used for the following form fields: Short Text, Long Text, Number, Email or Website.
After adding a field to your form, click on it in the main view to open the Edit Field panel. Under the label name, check the Visibility box by choosing inside the field .