What does BBCode in my Message Forum mean? What can I do with it?

BBCode is a safer, easier and more limited way of allowing users to format their messages. This can be used to bold/italicize/underline text, as well as make links and display images. Some examples of BBCode are:

[b]bolded text[/b]
[i]italicized text[/i]
[u]underlined text[/u]
[url]http://example.org[/url]
[url=http://example.com]Example[/url]
[img]http://imageurl.png[/img]
[quote]quoted text[/quote]

More examples can be seen below:
http://en.wikipedia.org/wiki/BBCode