Forums are the ‘must-have’ component for every CMS/Portal system and as such PHP-Nuke developers had phpBB (probably the most popular forum software available on the net) built into phpNuke for your convenience.
In order to activate the forums module, you just have to log in your administration screen, click on modules and activate it using the activate icon as shown here:
Once activated, the module will be available for administration/management through your admin control panel -> Forums.