Ubuntu comes set up to not allow non open source software (and non free) (basically it won't work if it is not open source.)
how ever because the kind people who create Ubuntu realise that some of us want to use flash, java, and MP3 codec etc that we need to be able to use said software so they include an option to allow such software, codecs and so on.
It is so easy I'm going to do it in one step!
Step 1: the one and only step to doing this
look at the top of the screen,
choose system, go to administration and click on "software sources"
Ubuntu will ask you for your password so enter it. Make sure no one including the government is looking over your shoulder. *Puts on tin foil hat*
ok now it will open a program with some check box options, check them all, this will allow you to use all repositories, including the restricted and multiverse repositories.