I'd also recommend handbrake. Be aware though if you are backing up a commercial DVD you need a copy of the libdvdcss installed to decrypt the DVD. It is no longer built into handbrake but is contained in the VLC Media player, so you may wish to get a copy of this to.
You should only backup DVDs that you own. Even then you maybe breaking the law.
If you've never heard of handbrake here is a review of its basic use.
http://www.macworld.com/article/1157590/how_to_rip_dvd_handbrake.html
Another useful video format editing tool is mediastreamclip for exporting to different formats. (Free)
If you want to create DVDs toast/popcorn used to be popular, though I personally though they were overpriced.