Ok. I figured out that when you download tv-grab-file, you apparently have to rename it to tv_grab_file, otherwise it won't be recognized. They should probably fix that, so that when it's downloaded it will already be named correctly.
So now I just need to figure out where to put the xmltv file, and how to set up a cron job. I keep seeing others say, put the file in ~/.xmltv/, but which account? And what if I'm accessing tvheadend from a remote system? Either I don't seem to have enough information, or this is just way too complex for my feable brain! :)