Don't buy a plugin until you learn Rhino. If you've already
purchased a plugin like Matrix or RhinoGold, don't go through their
training until after you learn Rhino.
My suggestion is to go through these as fast as you can to get an
overview of the Rhino landscape. Then, go through them again. This
time, don't move on to the next topic until you have a firm
understanding as things build upon themselves. Google is your friend
and you can delve deeper into any topic.
You should also join the Rhino forums (v5.Rhino3d.com) and the CAD
jewelers forum (3Dcadjewelry.com).