Assuming you are a windows user....
Handbrake (hxxp://handbrake.fr/) is a simple to use and free program for mp4 conversion, I do no think it will convert copy protected material though such as Commercial DVDs or Blurays, to remove that copy protection you would probably need to use another application.
Something like Anydvd or Anydvd HD from hxxp://www.slysoft.com/en/ that application is not free but a 30 day trial is available. will remove DVD and Bluray copy protections. If you plan on converting and or watching numerous DVDs or Blurays on your computer it is worth every single penny. They also sell Clone DVD Mobile which would also probably do exactly what you want.
The combination of those 2 programs is superb if you are new to video converting, you will not find much better for a simple new user friendly process.
There is also DVDfab again not free nor cheap but again very easy to use. They do a couple of free apps hxxp://www.dvdfab.com/free.htm which work similar to AnyDVD only not as many copy protections which you could use in combination with handbrake mentioned above (IE rip the dvd to your hdd to remove copy protection with one of the free DVDfab apps then use handbrake to convert the files to the mp4 format you want). This method would be a bit more involved but still pretty simple, heres a guide...
hxxp://forum.videohelp.com/threads/303110-How-to-easily-convert-DVD-to-high-quality-MP4-MKV-H264-using-free-tools
Another totally free tool is MeGUI I love this app, though it is not as new user friendly as the above combinations it is alot more versatile once you know what you are doing. Grab that at hxxp://sourceforge.net/projects/megui/
There are more solutions but those are what come to mind immediately in terms of user friendly-ness and a combo of free and non free solutions, if you need more or further help just ask
You may also need to know details like the MAX resolution for video files your tablet will handle before encoding and MAX bitrate, if you dont have that info you will just need to experiment (maybe do a trailer or similar from your dvd first rather than the whole film to check it works and save yourself a lot of potential wasted time

. ).
Converting files can take time, so you will also need some patience
Best of luck and have fun.