Can I watch videos on Ubuntu?

I wanted to have a play with Linux and installed a copy off the cover of a magazine. It seems to work nicely, bute I cannot seem to watch any videos on Youtube, Vimeo etc. Can Ubuntu actually play videos?

How can I play MP3s on Ubuntu?

I switched my old computer to Ubuntu Linux and most things work quite well. However I can’t listen to MP3 music files of watch DVD disks – why not?