DVD+/-RW are rewritable. So you can write or burn, and you can erase. While the DVD+/-R, you cannot rewrite.
As for the minus and plus sign. From what I see, the + is compatible with the newer DVD players and such. While the - is compatible with more DVD players, with older DVD player models.
The + though, is less prone to errors and interference during the burning process. And the + is more accurate for high speed.
I would suggest this DVD burner:
Newegg.com - Sony NEC Optiarc Black 18X DVD+R 6X DVD+RW 8X DVD+R DL 18X DVD-R 6X DVD-RW 12X DVD-RAM 16X DVD-ROM 48X CD-R 32X CD-RW 48X CD-ROM 2MB Cache SATA 18X DVD±R DVD Burner, OEM Version - OEM
I have this one, and it works great. Not a single problem. And it's SATA.