How can I play content from a media server?

You need to install the package totem-plugins-extra. You can find it in the Software Centre or just use:

sudo apt-get install totem-plugins-extra

from the command line.

Now open Totem, go to Edit -> Plugin, check that the coherence plugin is installed.

In the dropbox of the sidebar select Coherence DLNA/UPnP Client. You should be able to browse your server from there.

You can find more info in the totem plug-ins webpage.