To play DVD’s on Ubuntu, follow the instructions on Ubuntu.com
Notice that there are two commands you must enter in a terminal. Unfortunately I just glanced at these instructions and neglected to run the second command. After you have properly installed libdvdcss2 then try watching the DVD with VLC. VLC will usually play just about any kind of multimedia file. (I don’t know if it will play Blu-ray since my computer does not have a Blue-ray player).