For the newbies the default player in ubuntu is banashee.
But I recommend you to try Amarok.
It can be easily installed from ubuntu software center or Synaptic
the geeky way
sudo apt-get install amarok
Also install the following codecs, the codecs ubuntu recommends is having some problem in my system, these are recommended by the amarok developers.
sudo apt-get install libxine1-ffmpeg gstreamer0.10-plugins-ugly
Also try clementine and exaile two mediaplayers inspired by amarok