Pokerth is currently very much a "play with a few friends" game. Currently, there's nothing resembling a central server.
So you have to host a game yourself for your friends, or tell a friend (preferably a friend who is network-savvy enough to know what his internet ip-address is and if necessary, how to forward ports on his router) that he should host a game for you and your friends.

Check this thread about how to host a game:
http://www.pokerth.net/component/option,com_joomlaboard/Itemid,58/func,view/id,548/catid,13/

Sometimes people will host a game and post an announcement on the pokerth website about this. Check the homepage, the Latest sessions section in particular.

Hope this helps at all,
heyn