Autoresponder install help

I'm trying to get a sequential autoresponder working in Php List. I'd like to run Chui Tey's plugin and I've read through the documentation and don't see anything about what to do with a diff file. I see from a google that a diff file is a difference between two versions. What do I do with the diff files? I'm assuming that I should apply the diff file, but I don't know which file I apply it to, or how I apply it. Is there a plain english explanation that an intelligent person who lacks knowledge in this specific area can follow?
Thanks for any help.
Thanks for any help.