Thanks for the awesome response Mary!
David - You can look into merge fields which grab data from a particular field in a table. For example, using the Customer.FirstName merge field will display the appropriate customers first name in the email in place of that merge field. Customer representing the table, and FirstName representing the value held in that field for the screen active RecordID.
Check out the Automatically Merged Fields section of our Help Center article for some more info. Another thing you can do is make a copy of the CRM_NewActivity screen, then edit the screen and check out the actions in the first Save button on the screen. Look for the Character Function actions where you'll see the merge fields being made available to be utilized on an email template sent from that screen.
- Ashur