DVD disk What are the differances +/-

I was just wondering if someone could help me figure out what the differances are between DVD-R and DVD+R. I have another question while I’m at it about dual layer DVD drive burners, I assume that these drives are the latest in technology? Is there a place on the net that I could go too to read about cd media and the drives that go with each format.
Thanks for your time in reading my thread…

Mike