VWN
I also had difficulty at first and they don't come with instructions!
For an example, let's say you get a 60 degree 'from' reading on the VOR.
Align 60 degrees on the rose of the plotter with the distinct blue North (magnetic) arrow on the VOR rose.
The arm of the plotter now gives you the line to draw on the chart which is the 60 degree 'from' line. Do the same with a different VOR and 'hey presto' the intersection is where you should be.
I bought mine because, early on, I had difficulty making an accurate asessment of the angle on the blue VOR rose on the chart, and they are sometimes obscured with other information and difficult to read whilst keeping straight and level etc. I don't use it in practice, however, because it is just one more thing to drop in aircraft whilst fumbling around.
The way I got around this was to buy a pack of those self adhesive, flexible and transparent compass roses and I stuck one of those over the 3 VORs that I used the most. This enabled me to locate the angle much more quickly and to just use a ruler to draw the bearing. It is just a case of finding what works for you.
Incidently, I also use the stick-on rose on my chart to make an accurate initial estimate of track when doing diverions etc. and I find that by using a ruler and sliding it from rose to current position I can estimate track to within a few degrees very quickly.
Hope it helps.