They are different formats similar to the way there were different formats of videotapes like VHS and Beta. Depending on your hardware, it may support one, or both formats.
You can go here for a more in depth rundown if needed.
It's quite common for most people now-a-days to be able to use which ever type they choose. I'm sure there are exceptions, but all of my burners are + or -. And if it is a + disc or a - disc, once again, most players will play either.
It should say either on the box or right on the front of your burner.
Minus (-) seemed to be the one that the industry took to at first... I think, so many people started with those.
But I use Plus (+), because you can "Booktype" a plus disc to convert it to the equivalant of a DVD-ROM, which is the Original format. So by booktyping a disc, you have no worries of which player to play it in, because the player will think it is the original movie. No compatibility issues!
*Note*
Do yourself a favor Always use Quality disc's and burn slow. It's not a race.
Quick Check: This may vary, but for mine, when you are in Nero, at the last page, before you click the "Next" or "Burn" Button, there should be an Options Button. Check to see if the option is there.
To Booktype a disc, basicly, you have to create an ".iso" file in DVD Shrink, instead of all the .vob files. Then burn as usual with Nero.
But to explain in more detail, just do a search on this site. It's not hard to do, so don't worry.
Some drives can be set to automatically booktype via the firmware. All my NEC's are set to booktype every +R I burn to DVD-ROM without having to change anything in Nero.
Best way to tell if your burner can do this is to read the manual, or info about it available online.
