You need to go to 'All Pages' in the wordpress dashboard area and then go to the page that you have assigned the forum page to.
Then look again at neto's post. If you can't see the title 'Discussion' under the editor area then you may need to look at the top right at the tab 'Screen Options' and make sure you have the 'Discussion' box ticked. Then as neto says go to that and untick comments. Hope this is clearer.