If you just got it and its a new one then it doesn't matter - all the new ones do both + and - and often RAM too. I however don't know what the difference is, sorry.
Well dvd-r are cheaper to buy (cds) but the burners arnt. My dvd+rw was cheap ass from america and the disks are dearer than dvd-r's. and theres many differences on speeds while writing. You may want to read some reviews on your burner and see which disks you should use
dvd-r and dvd+r are just different formats. I know that dvd+r is a newer than dvd-r, so that's why some older players won't read those disks. Check the book on your buner, it will tell you which type of discs it can read/write.
DVD-R tends to be more of a standard, DVD+R is almost like always using CD-RW media, where you have to format the disc before use and create the file system.