Hi rae,
Adobe dropped Flash for Linux support so you will get weird messages from time to time, if you want to watch live online UK TV, go here:
and click on UK live TV and select a channel!.
Things like the package "libdvdcss2" are out of the hands of Canonical because it is a licencing issue, if they pre-install codecs for DVD playback, it can cause problems in some countries so it is left out but is available to install on demand! (some versions of Linux pre-install it anyway!). 
A complete beginner should start with something like a beginners guide of which there are many around on the web!. An example below:
A simple web search can often bring an abundance of info like DVD playback!:
https://help.ubuntu.com/community/RestrictedFormats/PlayingDVDs
The package "libdvdcss2" was added to the Software Boutique by the Ubuntu Mate devs and isn't sanctioned by Canonical as far as I know!.
Lastly, any questions relating to this or any other version of Linux can be answered on their respective forums of which I am sure you are well aware!. 