Once you have it connected properly per the following FAQ, you press "record" on the DVD recorder and "play" on the PVR when you wish to record. (you can have the programme you wish to record all set to go and paused at the starting point. You then press record on the recorder and play on the PVR at roughly the same time.)
Many people have found that the "copy to VCR" function (if it exists on your firmware) doesn't work very well, so just do the recording at a time you don't need to watch.
Here's a useful post - FAQs, Search Tips, Optimization, etc: