I want to record onto DVD?

I don't understand DVD+RW verses DVD-RW

They are just two different methods of making DVDs... the + uses one kind of dye and the - uses another... some recorders and players are fussy when it comes to which format they will play... you will need to find out if your particular DVD player is fussy or not.

Does my DVD have to be 16x to get 6 hours?

This spec has nothing to do with the amount of recording time... the 16X (or 2.4X; 4X; 6X; 8X) are all a measurement of how much data can be written to the DVD SPEED-wise. An 8X DVD takes twice as long to burn as a 16X one.

Do they make ones with more than 6 hours?

The amount of hours that will fit on a DVD is directly proportionate to the compression and whether the DVD is single layer or dual layer... or even blue ray.

What does it mean if it's 4.7 GB

Single layer DVD is 4.7GB, dual layer is 9.4GB and blue ray is way up there... most DVD burners these days are dual layer.

So... the best way to do this is just to get an external USB tuner box that gives you the ability to hook up RCA jacks (which is what comes out of your VCR) and it will allow you to dump all your VCR tapes to the hard drive of the computer. You can then use Nero (or some other software) to "re-master" the video and audio into a DVD format that you can burn on to DVD and use in DVD players... its not as bad as it sounds... once you have it down you will be an expert!