What is the difference between a dvd +r and a dvd -r

At the very basic leve, the substrate is different. There's also the fact that DVD+r is more tolerant of slow data streams (buffer under-runds) and can wait for the next byte while, as we all know from so many coasters over the years, DVD-R can't.
So, while DVD+R are technologically superior other technologies have overtaken the problem: Dual and Quad core processors, buffers to overcome the buffer under-run etc.