After the donation/sale, an email thanking the donor is generated by the system to confirm their donation. Like a mail merge, the emails pull data from the system using the Merge tags in the [brackets].
To edit confirmation emails:
Go to: Admin > Site Settings > Online Donation Forms > Donate Cash and Online Store > Edit the Pay Now Email and Edit the Pay Later Email
The default template uses merge tags such as [event_name} and [organization] to allow the emails to be sent "out of the box". When editing, it is easier to replace these with plain text than to locate the source to edit.