Discs that are 'R' are recordable only once
Discs that are 'RW' can be erased and reused
The '+' & '-' are different recording formats invented by different companies. Therefore some DVD recorders can only record one or other of the formats, although many PC drives can now record both. There is also a third format called DVD-RAM that is rerecordable, but very few players can even play these discs.
Once a disc has been recorded it can normally play on most DVD players, regardless of the origional format. There are however a few older players that wont work with some or even all of the recordable discs.