Occasionally you might not have to rip the DVD, to test whether you need to, try this: if you open a DVD in My computer, there's usually two folders, inside hte Video_TS folder, there'll be a whole buncha files, including some big ones with the extension .vob. Copy them onto your computer and change the extension to .mpg or .mpeg and try to play them like regular video files, which is essentially what they are, and see if that works. This doesn't always work due to encryption or how the DVD was created, but it can save some time versus ripping them.
If not, then you'll prolly have to rip the DVDs, for which there is info here:
How to Rip DVDs - WikiHow
Alternative (easier) way:
DVDShrink DVD Shrink freeware download
HTH!