vBulletin Manual - Adding or Editing an Announcement

To add an announcement, go to Announcements > Add New Announcement. This form will be displayed:

Forum – the forum which this announcement will be displayed in. All Forums makes this a global announcement. Note that if you select a specific forum, the announcement will also be displayed in its child forums.
Title – the title of the announcement. This will be displayed on the thread listing and is what users will see before they are displayed the text of the announcement.
Start Date – the date when the announcement will begin to be displayed.
End Date – the date when the announcement will stop being displayed.
Text – the body of the announcement. You may use smilies, BB code, and HTML, provided you have set the appropriate option below.
Reset Read Status – The read status determines if an announcement is displayed on the "New Posts" and "Today's Posts" searches. Once an active announcement is viewed, it no longer will display on these searches for the user. When this option is set to yes, it resets the status of the announcement for all users so that they will see it as a new announcement again. This option is only available when editing an existing announcement.
Allow BB Code – set this to yes if you want your announcement to be parsed similar to posts. Not only will this allow you to use BB code tags such as [b] and [img], but all line breaks will automatically be converted to HTML line breaks. If you set this to no, then you must enable HTML and use <br /> for line breaks.
Allow Smilies – setting this to yes will cause smilies such as :) to be parsed into the appropriate images.
Allow HTML – setting this to yes will allow you to use any HTML in your announcement. Note that if you have set Allow BB Code to yes, then any line breaks (even within HTML markup) will be automatically replaced with <br />. If you enable this option, it is recommended that you disable Allow BB Code and simply use straight HTML.