Placeholder text is text displayed within a standard short or long answer text field as well as email and phone number fields. It can be used as a substitute for a field label or can provide more information about the information that needs to be collected by that field. The grey text will disappear as soon as the end user starts typing.
Note: This feature is only available on v3 forms. For more information on updating your forms please see this doc.
To add placeholder text click on the field, then type in the text you want to show within the field into the "Placeholder" text box on the left side of the builder.
If you'd like to use that text as a replacement for your field label (just in case you need to make your field names equivalent to the CRM you're passing data to), just change the label to whatever you need it to be, then click "Hide Label"