Recording from DVR to Cassette using this?

Well, generally, you simply need a Cable of the RCA 3way A/V cable variety, usually with Red, Yellow & White RCA plugs on the end... there should be corresponding RCA Sockets on each machine.. Plug the leads in colour to colour, then insert tape in VCR and select the Auxiliary Input (Or whatever input it is actually called) to Record from... start
"Recording"

Then on the DVR start "Play" and ya should be all up & running.

What I do first, is set it up on my TV first, using the RCA sockets, set it up so it is all playing clear picture etc.. then I connect up to the VCR.

NB: There are "Other" types of "Inputs & Outputs" among them ones called "Composite Video" "S-VHS" "SCART" ALL of these have standard interconnect leads, so if on your machine you DO NOT have the RCA Sockets.. but have one of those "Other" simply procure a Male to Male Cable of that type & then simply substitute the alternate "Cable" for the "RCA" & the rest is the same.