Heartland and ZenCart

has anyone gotten these to work together? I have the "instruction manual" (as well as the "web connect" login stuff) from Heartland, but it makes absolutely no sense to me. I can't find a way in the ZenCart back end to add a module - and it LOOKS like Heartland wants me to replace all of the Zen Cart checkout pages with theirs. I'm totally lost with all of this - I have no idea what I'm supposed to do here. I found a couple of other threads on Heartland, and how difficult it is to set up - but neither are "resolved" and I don't know if that's because the OP never bothered to come back and update, or if they are still having issues.

If anyone can point me to a tutorial, or code or something that can help me with this, it would be appreciated.

Thanks!