The VB that you have heard of is probably vbcode, which is used in the vbulletin forum software that this site uses.
It has nothing to do with visual basic.
It is actually a set of custom tags for use with formatting in forums.
Allowing html in posts is not always a good idea, so php has a function called htmlentities() that takes any input the user gives it and converts any html tags or reserved characters and translates them into their respective html entities, such as <a> becomes <a>.
To still allow users to post formatted messages, you then have to come up with an alternative tag system. For example,
some text[/b/] on this forum makes "some text" appear bolded (if you remove the "/" character in the closing tag).
The way this works is that when the information is read from the database and it encounters one of these tags, it replaces the tag with the real html tag so the text appears formatted in the users web browser.
Did this explain it thoroughly enough?