Custom receipting is made up of two main parts -- the "Thank You" message for a specific giving form and the "Email Template" which is the wrapper for the email that has your logo, address, etc.
For each giving form you determine from "who" the receipt is emailed, if anyone internally will be BCCd on the receipts, what the subject line says, what the "Thank You" message says, and what email template is used.
The "Thank You" Message
Each giving form has its own receipt message. This message will be included in the email receipt above the part where we include the transaction details.
This is where you can include tax information or any language specific to that giving form.
The email template is the wrapper for emails and is built through a drag and drop interface. You may have multiple email templates and apply them to receipts as needed. Most clients generally have one email template that all forms leverage.