The first thing you are going to need in order to rip a DVD on a Mac is the excellent and free software called HandBrake. In the developers own words "HandBrake is an open-source, GPL-licensed, multi-platform, multithreaded video transcoder, available for Mac OS X, Linux and Windows". The important bits that you Mac users need to extract from that is "Mac OS X", "open-source" and "multithreaded video transcoder". Take a look at Group test: what's the best video-conversion software?
Once you've downloaded HandBrake for Mac, the rest is refreshingly straightforward and simple to use. Here's a step-by-step guide to show you how to rip a DVD on a Mac.
How to rip a DVD on a Mac
Download the latest open-source version of HandBrake for Mac and open it.
Enter the DVD you want to rip into the optical drive of your Mac and click the Source button, that can be found in the top left of the HandBrake window.
You can edit the ripping output of your video by clicking on Toggle Presets and/or Picture Setting, found at the top right of the window. Here is where you need to select the DVD you want to rip.
The next thing you need to do is select the title on the DVD that you want to rip. More often than not DVD with have multiple titles, so this may require a bit of intelligent guesswork and some trial and error.
All that is left to do now is select where you want your ripped video to be saved. This is done by clicking on the Browse… button to the right of the window and selecting the appropriate folder.
Click Start and let HandBrake do the rest.
Note: Remember to abide by all copyright laws when using HandBrake.