You need forum / forum_topic / forum reply classes.
After create some forums in your web site, eZ publish use the default templates. In the design "standard", you can find the basic templates to display a forum, forum_topic and forum_reply.
After, you can override the default templates, and customize your forum like you want.
Or you could use the pre made classes and templates laying around.
I guess you installed 'plain install' witch means no content and almost no classes.
So classes for plain install can be found here: http://ez.no/download/ez_publish/ez_publish_3_stable_releases/3_8/packages
If you want the newer classes used in ezwebin, you can go here: http://ez.no/download/ez_publish/ez_publish_3_stable_releases/3_9/packages/3_9_2