Very simple question: converting DVD/VOB to (say) AVI
I suggest you use Handbrake. It's one of the best transcoders I know of, and have used it myself many times to convert DVDs to video files.

It is pretty simple and straight forward to use, but if you need any help/guidance this page covers pretty much all you need to know. 

Have fun! And if you have any further doubts don't hesitate to comment. 

Kevin.