what are the basic differences between  DVD+R ans DVD-R formats?
Which format allows doble side recording?

Here is a minor Breakdown for you..

DVD-R and DVD-RW
DVD-R was the first DVD recording format released that was compatible
with standalone DVD Players.
DVD-R is a non-rewriteable format and it is compatible with about 93%
of all DVD Players and most DVD-ROMs.
DVD-RW is a rewriteable format and it is compatible with about 80% of
all DVD Players and most DVD-ROMs.
DVD-R and DVD-RW supports single side 4.37 computer GB* DVDs(called
DVD-5) and double sided 8.75 computer GB* DVDs(called DVD-10).
These formats are supported by DVDForum.

DVD+R and DVD+RW
DVD+R is a non-rewritable format and it is compatible with about 89%
of all DVD Players and most DVD-ROMs.
DVD+RW is a rewritable format and is compatible with about 79% of all
DVD Players and most DVD-ROMs.
DVD+R and DVD+RW supports single side 4.37 computer GB* DVDs(called
DVD-5) and double side 8.75 computer GB* DVDs(called DVD-10).
These formats are supported by the DVD+RW Alliance.

This is from http://www.videohelp.com/dvd.htm

http://www.anandtech.com/guides/viewfaq.html?i=118

This site go into more detail about the difference between the various
DVDR formats. Hope this helps.