A Merge Field is a field you can put in an email template to incorporate values from a record. For example, you can place a merge field in an email template so that the greeting includes the recipient's name rather than a generic “Hello!”.
This will only work for Engage Emails.
It will not work with Order Confirmation Emails, but you don't really need to add them anymore as most of these fields will appear in the email.
Some of the merge fields will not work on other recipient lists as those contacts may not have those data in their record. (e.g. $TicketTypeName will not work for emails sent to auction participants as they do not have tickets.)
If you're sending an Engage Email to your attendees, you can personalize those emails by adding these merge fields to your email:
To see this list you can also click the Help Center button in Engage.