From Online Manual
If enabled, the forum news will show in the header of the forum. The news will display the content of the text boxes found on the news management page (Administration Center > News and Newsletters > News). By default, it says “SMF - Just Installed!”.
Additionally, a news fader box can be displayed on the Board Index that will fade news items in and out of view. This is done so the page doesn't have to be refreshed like the main news does. The admin can enable the news fader and change the fade time by visiting the Current Theme section of the Administration center, and selecting to Show News Fader on Board Index.
To edit the news displayed, the admin simply needs to edit the text inside the text boxes supplied on the news page. Both Bulletin Board Code (BBC) and HTML can be used to format the news in these boxes. To create more text boxes for news items, the admin must select the Click here to add another item link located at the bottom of the news page. They can also delete news by selecting the check boxes beside each of the news items that is to be removed, and select Remove Selected.