Basically a -CG is where you get a near invisible leader of negative charge move from cloud to towards the ground. From the ground a positive charge - a streamer moves up towards it. When they touch each other the current flows, flowing from ground to cloud. This can happen several times very very quickly causing the flicker you sometimes get.
With a +CG the charges are reversed. They tend to be associated with much more powerful strikes and are thought to be substantially less common than -CG ( negative cloud to ground). They tend to be that single really loud earth shaking strike that you get - single stroke.
I think the +1C is intracloud lightning. I'm just sorting out my java so I can have a look at the IOW site.