The Fields tab lists dynamic (merge) fields you can use in your delivery document. These fields represent actual values in the Traverse database. When you add them to your template, when the email is generated, the value in those fields will be inserted into the email.
NOTE: If you use TPS, the additional customer-related information available for the TPS Receipt document (Customer Name, Customer Address 1, Customer Address 2, Customer City, Customer State, Customer Zip Code, Customer Country, Ship To Postal Code, and Ship To Country Code) is limited to the content submitted to the payment provider. Changes made to billing information within the payment provider UI are not typically returned to TPS and may not be reflected in the data available on the document deliver template.
To add a field to your email template, drag the field from the tab and drop it into the Subject field or the Body of the email. Dynamic fields are indicated by brackets.