I am stuck and lost.

I am wanting to modify tge enail sent to my customers after checkout to include the new UK DSR regulations, but I have hit a brick wall. I have tried to follow the code in the pages that make up the email components however I cannot follow them. I have searched the FAQ & Wiki for answers but drawn a blank. So I have a couple of questions (sorry);

1. What is the subject that I should be searching for in the FAQ & Wiki?
2. Should I ‘define’ what I want to say in checkout_process.php and then call that statement in order.php?

Once I have made the changes I can then upload them for zencart community to use.

Thank you for your time